By Dave Hobbs. Air-conditioning service stinks sometimes. Let’s face it. I mean it sometimes stinks literally – like bad odor stink. Those of us in the warmer and more humid climates regularly run into customers complaining of a foul odor that emanates from the dash. Your customer today is driving a 2003 Chevy Trailblazer and describes their complaint as this terrible musty odor. When you climb inside the vehicle to confirm the complaint, your nose causes the rest of you to want to do a 180, but you know it’s going to be your job to turn this foul odor into a profitable job. You are all too familiar with the cause and the fix.

The cause is microbial growth taking place due to moisture building up in the evaporator housing. You look for the usual suspects of a missing, pinched or restricted evap drain, but it’s not the case this time. Convention says use one of those products (such as AirSept’s Cooling Coil Coating) that clean the evaporator. Then, maybe add an afterblow module that will run the blower motor a few minutes after the key is turned off, to dry off the evaporator core to prevent the return of the nasty odor. You consider making that phone call to your favorite parts supplier when it occurs to you to check TSBs (Technical Service Bulletins). After all, you’ve performed the first two preliminary steps in any diagnostic process – you’ve verified the customer complaint and done a quick inspection. The next stop is your trusty ESI (Electronic Service Information) system.

Turns out there is a TSB for a musty smelling A/C. You’ve seen GM’s and other OEMs’ TSBs for cleaning evaporator cores and adding afterblow fan motor modules, but today is different. TSB 05-01-39-002A describes a musty odor from the HVAC being repaired with a reprogram of the HVAC control module by enabling its afterblow function with new software.

Welcome To The World Of Flashing!

Flashing (as it’s commonly called) or reprogramming EEPROMs (as you might more formally call it) has been around for years. In the late 80s and 90s, most of this work was performed with factory scan tools. Don’t own factory scan tool? Then you guess it may have to go back to the dealer. But you’re too short handed today to take the vehicle to the dealer yourself, so you may have to send your customer to the dealer. You hate doing that. The dealer might just lure your customer away permanently. This whole scenario with the 2003 Chevy may not be a problem at all, if you are willing to invest in something called a J2534 Universal Reprogrammer and get some training on how to use it. Intrigued? Read on!

Is There a Business Case?

Many of today’s service fixes, including the HVAC odor TSB just mentioned, are accomplished with software updates. Improvements to drivability, false DTCs, even making parts last longer, are often done with software. Years ago, modules were either changed via part number supersessions, or a pluggable EPROM was removed and replaced by the tech. This was not efficient for the OEMs to do under warranty, so they migrated toward modules that could be reprogrammed electronically. For years, new car dealers have enjoyed the ability to simply program new software into an existing module with a CD/DVD-ROM, or over the Internet using their factory scan tools. This gave them an advantage over the independent garage that had to work on several makes of vehicles and couldn’t afford all the factory scan tools required to keep modules up to date with the latest software. The EPA wants independent garages to keep cars running clean with the latest software, because that’s where most cars go when out of warranty.

While some OEMs only allow for mandatory powertrain module reflash ability, other OEMs have bumper to bumper J2534 compliant modules. Everything from engine and transmission, to HVAC and suspension systems, can be flashed on some vehicles (including, of course, the HVAC module in need of new software on the 2003 Trailblazer). Conservatively speaking, 1 out of 10 vehicles (’96 and newer) have an ECM/PCM software update available. Some studies say the number is as high as 7 out of 10. And some 2008 Chrysler vehicles have 40 processors, while BMW 7 series vehicles have over 100 processors. However you slice it, that’s a lot of potential business for anyone’s shop. It’s one job on a vehicle that does not require you to open your tool box, set the lift, or even require a service bay. No parts need to be stocked, so space and inventory tax are not factors.

What is the ROI (return on investment)? By seizing that one in 10 opportunity, a typical shop that works on three cars per day should gain back its investment in a few months, and a net profit within the first year. Other shops that are reluctant to send their customers to the dealer may want to sublet out the labor for flashing to a J2534 equipped shop. And the best part – no factory scan tools are required for J2534 flashing. Don’t get me wrong, I love factory scan tools and own several myself, but I simply can’t afford them all. So for those occasions when I need to flash a Ford or Toyota, I have a J2534 universal pass thru reprogrammer. I train aftermarket techs every week, averaging about 30 techs per class. When I ask for a show of hands of shops that own at least one factory scan tool, I usually get one or two hands. When I ask the same question about J2534 programming equipment, no more than one hand goes up. What does that mean to you? It means there is opportunity and very little competition in this area. What are you waiting for?

So What Exactly Is J2534?

J2534 is an SAE (Society of Automotive Engineers) standard for pass thru programming of computers on passenger cars and light trucks. J2534 was established for 2004 and later vehicles. The SAE document provides a framework for the interface between a tool and the vehicle. The OEM can decide the scope and method of module calibration downloads from the Internet or a CD/DVD-ROM, and the tool manufacturers can decide the interface between their tool and the PC (USB, RS232, wireless, etc.), which means there are going to be some variations on how each vehicle and each J2534 device on the market works out the flashing process (Figure 1).

For powertrain related modules, it is mandatory that OEM’s provide access to their software calibrations. It’s not mandatory for non emission related devices, so it will be hit and miss on whether you’ll be able to reflash an HVAC module or BCM on some models. GM is one of the OEMs that allows for bumper-to-bumper reflash, some even going back into the 90s, while Chrysler allows only for powertrain module reflashes. J2534 is also an evolving standard, as it changed to J2354-1 in April of 2004, and then again in March of 2006, when it became J2534-2 (to allow for more serial data bus protocols to be added). When shopping for a J2534 reflash tool, look for the latest standard, to ensure better coverage of vehicles.

Flashing, Configuring/Coding and Relearning

Not every one of those 1s and 0s inside a module’s head gets there the same way. In the case of J2534, there are some types or memory that aren’t completely erased and reprogrammed. Due to the small amount of data involved, there are “mini” programming procedures (that often involve only one block of memory data) which are completed without access to the Internet or a calibration disc. A scan tool is all you need for these cases. What are these procedures? European OEMs often use the term “coding,” while other OEMs may use the terms “configuring” or “module setup.” With the European car market, many aftermarket scan tools with the ability to code modules are coming along side the OEM factory scanners (as is the case concerning configuration procedures with many non-European OEMs’ modules).

An example of configuration would be the familiar adding of factory accessories. Let’s say you want to add a set of factory fog lights and your customer ’s vehicle utilizes the BCM in the process of controlling the fog lights. If you just bolt them on and plug into the factory wiring harness, the BCM still doesn’t know they are there, because the vehicle was built without fog lights. Using a scan tool (many times, only a factory scan tool will do the job), you connect and communicate with the BCM. Then select the appropriate RPO code and activate the option (Figure 2).

Relearning is similar to configuring and coding, in that it doesn’t require an Internet download or CD/DVD-ROM file. Examples would be idle learn, cam crank variation relearn, and fuel trim reset – procedures that most drivability techs have performed numerous times. Most aftermarket scan tools are capable of these relearning duties. Certain models, you may or may not be able to relearn, reset, or reconfigure with an aftermarket scan tool or the J2534 reflashing tool, so once in a while, a trip to the dealer is still going to be inevitable. The same is true for vehicles with certain immobilizer systems. An example would be Dodge Ram Cummins diesels – when programmed with a J2534 pass thru device, they will have to have their vehicle theft deterrent system (SKIM) programmed with a factory scan tool, unless a person at the local dealer decides to help you obtain the security code via the VIN. Everyone will agree that no matter how universal a tool is, there are always going to be exceptions where it doesn’t work. In most cases however, J2534 really works!

What Do I Need To Buy?

Since J2534 requires no factory scan tool, but rather a PC and an Internet connection or a file from a CD/DVD-ROM, you’re going to need the J2534 tool, a PC with a DVD-ROM, high speed Internet access, an e-mail account, and access to factory calibration software.

First, investigate the various J2534 programmers on the market (Figures 3, 4). You will want to see if they are compliant with the latest standard (J2534-2) and whether (or not) they are able to do off-board reprogramming. What’s off-board programming? It means a Pass thru tool has available a set of connectors that fit the most popular ECMs/PCMs, allowing for serial data, power, and grounds to be connected to the module while it’s outside of the vehicle.

To get modules as near as “plug and play ready” as possible, most parts stores that carry remanufactured ECMs/PCMs have a J2534 tool with an off-board programming cable set. There are some cases where off-board programming is beneficial, and some where it won’t work due to the manufacturer’s requirement to program the module in sequential order with other modules. Off-board programming cables don’t exist for non engine control modules, so the 2003 Trailblazer ’s HVAC head that was discussed earlier could not be flashed out of the vehicle. Take into consideration whether you might want to program engine control modules offboard. (Note: Not every J2534 tool has the option to buy off-board reprogramming cable sets.)

Once you’ve selected the J2534 tool, move your next focus to obtaining the right PC. A laptop PC is preferable to a desktop PC, due to the flexibility of where you can do flashing. Unless you purchase one of the more expensive ruggedized laptops (such as the Panasonic Toughbook®) you will need to admonish the techs in your shop to practice care with it. You can’t lay it on a filthy seat (the cooling fan will suck up dirt), you can’t pick it up by the screen (don’t ask me how I know this), and you can’t drop it.

Hardware requirements for the J2534 PC are not that demanding. A general rule of thumb is if it’s been built in the last two or three years, it’s probably good to go. Pick out the big volume OEM vehicle brands you see in your shop and visit their service website sections for J2534 hardware requirements before you start shopping for a PC. Both the OEMs’ PC requirements and J2534 tool makers’ requirements must be followed (Figure 5).

I also would recommend a “real” PC, not a mini net book or an Apple/Mac. I love my Mac and run a program on it that utilizes a virtual image operating system with Microsoft Windows XP and Windows Explorer, but I’ve never bothered to try to flash with it. I guess I’ve seen one too many Apple commercials where the PC guy and Mac guy are arguing about who’s better, and I don’t want that argument going on while I’m flashing a $500 control module. Just get a PC. If you have a PC that’s up to the task, make sure it gets reassigned to shop duty. Don’t try to dual purpose the laptop used by the bookkeeper as a flashing PC and office PC.

As important as the hardware is the software. However, as can be the case with PC based scan tool software, PC based flashing software from one vehicle manufacturer can have compatibility issues with that from another vehicle manufacturer. Operating system conflicts and PC terms like MS Java vs. Sun Micro Systems Java, cookies, pop up blockers, firewalls, spyware, antivirus programs, etc. are likely to be issues you’ll have to tackle. You may be thinking that these things are best understood by techs qualified to moonlight for the Geek Squad, so there’s no way you’re going to be able to do this flashing thing if this level of computer knowledge is required. But don’t stop reading – you CAN do it!

The details concerning what goes on inside your computer will typically be worked out when you perform the initial PC setup and installation of the various OEM software programs required to do flashing. It will kill a day or two of your time and will require persistence and good support from the J2534 tool supplier. It’s amazing what some J tool suppliers’ support teams can do these days. They can actually connect to your PC from offices several hundred (or thousand) miles away and see your frozen screen and control your mouse. That has been a lifesaver service for a computer challenged tech like me. In this day or two of setup, you’ll also be setting up a particular bay in your shop that can be utilized for flashing. Most OEMs require their calibrations for flashing to be downloaded from the Internet, so a high speed Internet connection is not just preferable, it’s an absolute. If you choose to go with a wireless connection, that will be fine, but make sure there’s nothing that will block the signal. I’ve heard of cases where there was a wireless router in the shop, but between the router and the bay used for flashing was a bay used for motor home repairs. A great big metal object like a Winnebago is not exactly conducive to the clear transmission of wireless Internet signals.

Next, you have to get the PC with the Internet connection linked to the vehicle via the J2534 pass through device. Most use a USB cable (Figure 6). Also, while it can be really handy to have a PC based scan tool communicating wirelessly from the DLC to the scan tool, I don’t advise doing that while flashing. Too many things can go wrong, and you really can’t afford to brain dead an expensive module.

In your flashing bay, you’ll need a battery charger that is kind to the electronic modules being flashed. If battery voltage gets below 12 volts while flashing, the module being flashed could be damaged, so you must keep system voltage levels up while programming. The average battery charger puts out voltage levels that can be too high, as well as far too much electrical noise. Snap-On and Midtronics produce battery chargers suitable for flashing. This rule for good clean uninterrupted power applies to the PC you use for flashing too. If you use a laptop, make sure it’s plugged in and not dependent on its own batteries. Disable screen savers too. You don’t want the PC taking a break in the middle of flashing.

Software Time

Now that you have the J2534 device, a suitable PC and a good Internet connection, and a way to keep the vehicle’s battery properly charged, let’s turn our focus to the software you’ll need to purchase. First off, you’ll install the software that either comes in the box with the J2534 device or is available for download from the J tool provider ’s website. Nothing super tricky here – just follow directions and have the tool provider ’s phone number handy.

Next are the files you’ll need to load in advance, prior to your first flashing task from the vehicle OEM. This isn’t the actual calibration file that will go into the vehicle’s module, but rather, important files required for accessing and managing that particular OEM’s calibrations once you do get a vehicle in for a reflash. I strongly recommend going to the handy clearing house website www.nastf.org, to visit each OEM’s site that you think you might be flashing in the future. If you only see a particular make of vehicle once in a blue moon, you might skip the information on them. But if you see a lot of Toyotas, Fords, Hondas, Chryslers and GMs in your bays, go to their websites, get registered with a login ID and password, then download any calibration management software that might be required (you’ll need to supply an e-mail address to do this too). The time consuming work of putting in your name, address and other business info, along with obtaining the calibration management software, will be done in advance. Preparation is the key to success in making each flashing job profitable.

Now, with the J2534 tool software in place, along with all the OEM-required file management software installed on your PC, you are ready to flash.

To Flash Or Not To Flash

So you’re ready to flash, but how do you know when to justify doing it? Obviously, if you are replacing an engine control related module, the new or remanufactured unit will require programming. Many new and remanufactured ECMs and PCMs are sold without engine start calibrations, so you really don’t have a choice here. If you or your customer opts for a salvage yard part, the same applies, even though it may start the engine. Fine details like engine RPO, VIN, tire size and axle ratio are contained in the end model calibrations inside the used engine controller ’s EEPROM. You’ll need to put the right stuff in it for your customer ’s vehicle.

Also, recall the smelly evaporator in the 2003 Trailblazer? Of course, that complaint was listed in a TSB indicating a calibration related solution. In a case like that (once again), its time to go flashing. But how do you obtain the actual calibration?

Most OEM websites are available with short term subscriptions. Typically, they range from very short terms (24-48 hours), monthly terms and yearly terms. Short terms typically cost $20-$30, while monthly are in the $100-300 range, and yearly, anywhere from $350 to $1500. Until recently, GM only allowed for yearly subscriptions, but they now sell a three-month subscription for $250 instead of a full year at $995. Tech 2 users who wish to flash and keep their Tech 2 scan tools up to date will have to subscribe for a year long term at $1395. The good news with the General is you can flash more than just engine controls, meaning our scenario with the HVAC controller flash to prevent return of the stinky evaporator can be accomplished with a three month subscription. If you get a lot of GM work in your shop, you’ll be getting you money’s worth after a few flashes.

Every manufacturer does things a little differently, so I’ll list a couple of examples.

Getting Chrysler Flash Ready

1. Subscribe to http://techauthority.com (Figure 7) and when inside the site click on “Flash.”
2. To download Chrysler’s file manager program, click where it says “Click Here,” then click on “Download Latest Application” and save to a location on your PC where you can find it easily. The download of a program called “DCX J2534 Update Manager” will take place first, then you will need to select “Run” for this program. This is the program which flashes Chryslers with the specific vehicle calibration software that you will obtain later (Figure 8). The first two steps are a one time only procedure and will not need to be redone on future jobs. Like many OEMs, Chrysler is one that only allows for the programming of engine controls with a J2534 tool. If you wish to program or reconfigure some other component, the factory scan tool will most likely be required.

The Actual Flash

1. Reopen Tech Authority and enter the part number you found on the ECM. Chrysler part numbers will always have eight digits with a two letter suffix. If there’s a calibration update, there will be a new two-letter suffix. Click on “Download” and click on “Agree” when a pop
   up window comes up next.
2. Close your Internet browser completely. The calibration is now on your PC, and you no longer need access to the Internet. Chrysler is somewhat unique compared to most other car makers in you don’t have to be online when the calibration is finally flashed into the vehicle.
3. Connect your J2534 pass through flasher tool to your PC and to the vehicle’s DLC.
4. Open the DCX 2534 Update Manager program. Click on “Select Pass-Thru” on the bottom left of the program and select the description of your J2534 tool and serial number (found on bottom of the J tool) to allow the DCX program to know which device you are using.
5. The rest of the procedure is to carefully follow the instructions that come up on your PC at the prompting of the DCX 2534 Update Manager program, as it performs its various procedures to flash the module in the vehicle (Figure 9).

Now you are pretty much done. Try to start the vehicle, and follow any other procedures recommended in the service manual, such as those related to theft deterrent or engine management relearns.

Getting Toyota Flash Ready

1. Toyota uses a DVD-ROM. Call 800-622-2033 to order from Toyota (Figure 10).
2. Install the program “Calibration Update Wizard” on your PC. A test screen will now come up. Read EVERYTHING – you must indicate that you have read it all before the DVD will allow you to advance. Most of “everything” is the usual advice and warnings we’ve already covered (Figure 11).

The Actual Flash

1. Check the vehicle to see if it already wears an “Authorized Modification Label.” If it does not, the ECU does not contain the latest calibration. Proceed with flash reprogramming.
2. Connect your J2534 flasher and open the tool’s program on your PC. Now click on “Analyze VIN/Current Software.” The flasher unit will basically run OBD II Mode 9 to obtain the VIN and calibration information.
3. Click on “Reprogram Controller.” Next, confirm the path for the software to move the calibration from the DVD to the vehicle via the J2534 device.
4. Carefully follow the Vehicle ECU Calibration Update Wizard instructions. If you fail to do so, the ECM may be damaged! You’ll be prompted to turn the key on and off at various times (Figures 12, 13).
5. Make sure you get a “Programming Successful” message when you’re done. Finally, install a dealer procured update label on the vehicle to let the next tech know the vehicle has the latest calibration.

These examples of Chrysler and Toyota show the differences and similarities between OEMs when it comes to using a universal pass thru J2534 flashing tool. After reading this, you’ll probably agree there are some come common threads when it comes to flashing:

1. You must be a technician who’s comfortable with computers.
2. You must be a technician who’s willing to carefully follow directions (oops, that leaves a few of us out)!
3. You must be a technician or shop owner willing to put in the time and monetary investments to carefully spec out, purchase and maintain a PC, J2534 tool, high speed Internet connection and most importantly, training for J2534 flashing.
4. Finally, you must be a technician or shop owner with a vision and sound business case for the growing future of module flashing.

Flashing is certainly not for everyone, and sometimes an article like this helps you determine that a particular service endeavor is not for you or your shop. If you’ve been reading this MACS Service Report and shaking your head no-no-no, we just saved you a chunk of money by convincing you to NOT purchase a J2534 flashing tool. On the other hand, if you are a visionary who wants to quit sending this fast growing segment of the service business to other shops and dealers, and you’re intrigued with the idea of making money selling parts (calibrations) that you never have to stock, then flashing may be for you. To help you even further, there will be two live training classes titled “Reflash/Reprogram/ Remobilize,” complete with flashing demonstrations, in Las Vegas next January at the MACS Convention. Hope to see you there!

Original article from MACS Service Reports, the official technical publication of the Mobile Air Conditioning Society Worldwide, Inc., P.O. Box 88, Lansdale, PA 19446. Click here to visit their website.

By Dave Hobbs. As a once-familiar gas jockey greeting passes into history, now-mandatory TPMSs have made it easier for drivers to monitor tire pressures. Servicing these systems is somewhat more complicated than operating a tire pressure gauge.

Myths abound when it comes to tire inflation. For instance, owners tend to believe they don’t have to check their tires once a month. Technicians sometimes believe they’re a better judge of how much pressure a tire should hold than the engineer who designed it. I’m probably in good company admitting that I check tire pressures on my personal vehicles only when I change oil—unless, of course, a tire looks low. Whenever I’m too busy to change my own oil, the tech at the shop I patronize lowers the tire inflation from the specified 36 psi to 32 psi.

Recently, there was a slow leak in my left front tire. After a cold snap, guess what? The tire pressure monitoring system (TPMS) light came on. If not for that light, I would never have known there was a problem with one of my tires until it leaked down to around 15 psi, which is where even a procrastinator like me recognizes that a tire looks low enough to check the air pressure. Thanks to the light, I aired up my tires and went about my business without incident. Unfortunately, that wasn’t a typical scenario just a few years ago for most vehicle owners, and a few paid the ultimate price for believing those myths about not checking tire pressures regularly.

Legislative Background

In September 2000, following several tragic accidents involving tire inflation, tire failure and vehicle rollover, a bill called the Transportation Recall, Enhancement, Accountability and Documentation Act (TREAD) was pushed through Congress in an amazing 18 hours and signed into law by President Clinton soon after that. Next, the task fell to the National Highway Traffic Safety Administration (NHTSA) to require automakers to implement the provisions of the new law by writing Federal Motor Vehicle Safety Standards (FMVSS) Standard 138.

The heart of the law affecting drivers and those of us in the service business is the section involving mandated systems to alert drivers to underinflated tires. Underinflated tires run hotter and have increased rolling resistance, which can factor into tire tread separation or blowouts. Phase-in for the TPMSs began in the fall of 2005 to mid-2006, with 100% compliance by the fall of 2007. (Vehicles over 10,000 lbs. GVWR, pickups with dual rear wheels and motorcycles are exempt.) Since this law was written and passed so quickly, there was no time for standardization within the industry, and the result has been a challenge for technicians.

Tire Pressures & Temperature

Although overinflated tires have their own set of problems, if your customers’ tires are as little as 41⁄2 psi lower than specs, their tread life (outside wear) is decreased by 25%, and fuel economy goes down 2%. Those numbers can double if the pressure is down by another pound and a half. Along with decreasing pressure comes decreased weight-bearing ability. Temperature has a big effect on tires as well. The lower the air pressure in the tire, the higher the tire’s temperature. Hot tire temps equal a greater risk for a blowout.

Cold ambient temperatures lower the pressure in a tire. For every 10°F drop in temperature, a tire can lose 1 psi. This means that if you get a cold snap one evening that drops the temperature 50°, your tires will be 5 psi lower. In a recent TSB, GM actually suggested adding 3 to 4 psi over the spec on the tire placard if you’re adjusting pressure in a warm shop and expect to send the vehicle into a cold environment. A special mention on tire specs: The maximum cold inflation pressure on the sidewall is not the recommended inflation pressure. It’s a maximum limit for the tire only. Check the tire placard/label (usually in the driver’s door jamb) or the owner’s manual.

About 85% of all tire leaks are like the leak on my minivan—very slow. According to the new TREAD Act/FMVSS rulings, a 25% pressure drop in tire pressure must turn on a tire warning light to alert the driver. A 25% drop in tire pressure is not easy to detect visually.

TPMS Sensors

There were two types of systems for detecting tire inflation prior to the phase in of mandated TPMSs—indirect and direct. The indirect TPMS uses no special sensors to check for a low tire, only enhanced software in the ABS module reading wheel speed sensors to determine tire inflation. A tire that’s underinflated is smaller in diameter, so it spins faster than a properly inflated tire. Because a tire on one side of a vehicle normally spins faster when the vehicle is turning, this software uses an average of the left front and right rear compared to the average of right front and left rear wheel speed sensors to determine if any tires are underinflated.

On the surface, these systems seemed like a good idea, but they weren’t without their disadvantages. This type of system can’t determine which tire is underinflated. In fact, if all four tires are underinflated, the system may not alert the driver at all. Also, with the indirect system, space-saver tires and even tires that are slightly mismatched in diameter or different from the factory size can trigger false TPMS warning lights.

The direct system was the other type of pre-TREAD Act system. These systems, which do use special tire pressure sensors, date back several years and are the type mandated by the new federal regulations. They use a small radio transmitter, most often mounted under the valve stem (photo 1), which communicates with a receiver in the vehicle. Two frequencies are used—315 and 434MHz. Each sensor broadcasts a unique ID, much like a cell phone’s electronic serial number (ESN). TPMS sensors come in numerous shapes and sizes. All are small, lightweight microelectromechanical sensor (MEMS) devices that contain sensor elements on an integrated circuit and contain a built-in nonserviceable lithium-ion battery that lasts seven to ten years.

Most sensors start to operate at speeds between 7 and 20 mph and sense within a 24- to 39-psi range. Their main job is to report a 25% or greater loss in specified tire pressure. TPMS sensors weigh about an ounce (28 grams), so doing a tire balance shouldn’t be a big deal. Most use aluminum valve stems at the end of the sensor. GM is one of the few automakers currently using rubber-stemmed TPMS sensors. There are almost as many brands and styles of sensors as there are vehicles. For example, Schrader/Bridgeport makes sensors for Ford, Chrysler, GM and Nissan/Infiniti; Beru makes them for Audi/VW, BMW Land Rover, Mercedes-Benz and Porsche; Pacific builds sensors for most Toyota and Lexus models.

Toyota has two physical styles of sensors—a 20° bend for aluminum wheels and 40° bend for steel wheels. Some Ford vehicles use a long hose clamp or band that encircles the inside of the wheel to hold the TPMS sensor in place, typically 180° from the valve stem to aid in wheel balancing. You may see the term banded applied to the Ford sensors, although many Ford sensors are the more common stem-mounted style.

TPMS sensors operate in different modes, depending on their commanded state and what the vehicle is doing (or not doing). They’ll be less active when the vehicle is not being driven, to save battery life. This mode is called stationary or park mode. The sensor will sample pressure only every 30 seconds on some models and may not send a signal at all to the ECU unless it senses pressure loss. Another mode— rolling or drive mode—occurs once the sensors detect movement. The sensors sense pressure every 30 seconds and transmit that information every 60 seconds in rolling mode. If a sensor detects a change in pressure of more than a pound or so, this sampling rate is increased.

If you disconnect the battery cable, the ECU will remember which sensor was in which location, but will forget the pressure values. This can lead to misdiagnosis if you’re looking at sensor pressures on a scan tool. Default pressure values read with some scan tools via the TPMS ECU are often a ridiculously low or high number until the ECU sees a valid information update after a loss of battery power. Just drive the vehicle above 20 mph for two to ten minutes and the ECU will have the correct tire pressure jotted down in volatile RAM.

Another TPMS sensor mode is called sleep mode. Vehicles built overseas may have their sensors in this mode prior to new-car dealer prep. Replacement sensors may also come in this mode and will need to be activated. Always write down the seven- or eight-digit ID from the TPMS sensor before installing it in the wheel. On the systems that require a factory scan tool to register the sensors, you may need this info.

Using tire sealant in a wheel with a TPMS sensor is a sure way to ruin it. There’s a small hole for sampling pressure and temperature that could very easily fill with sealant. If sealant gets in there, don’t wait for a failure, just replace the sensor. Just as sensors have antennas (photo 2) built in to transmit, TPMS electronic control units have antennas to receive. Toyota puts the TPMS ECU antenna and receiver in the roof of the vehicle. On the Toyota Land Cruiser, the TPMS ECU antennas are mounted in the outside rearview mirrors. GM uses the rear defogger grid as an antenna for its TPMS ECU antenna. They’ve had problems with micro-arcing across tiny breaks in their defogger grids, causing a frequency very close to that of the TPMS. The resulting RFI can turn on the TPMS light when the rear heated defogger grid is used.

Since most sensors use wakeup circuitry that uses technology based on centrifugal force, TPMS sensors must be mounted properly. If you get a sensor flipped upside down inside the wheel (and some will let you mount them that way), it may not receive the right centrifugal force on its accelerometer to wake it up, resulting in an illuminated warning light. Pay close attention to how sensors come out of a known good wheel and you won’t find this out the hard way.

Another less common type of accelerometer is directional in relation to the position of the sensor on the wheel itself. You might wonder how this could be installed incorrectly, since most sensors mount to the stem and the stem can go in only one place. Of course, that’s right, and you’d never see a problem on any of the four wheels mounted on the vehicle because they rotate. It’s the matching full-size spare tire using a TPMS sensor that could present a problem. On Mitsubishi SUVs, if you mount the spare tire on the tire carrier with the sensor/valve stem positioned straight down at the bottom, the sensor’s roll switch may turn on and keep the sensor powered up. This will convince the TPMS ECU that the spare is actually a rolling wheel. Mitsubishi advises mounting the spare tire with the sensor at or near the 12-o’clock position.

Instrument Panel Displays

All 2008 and newer models have TPMSs. On older vehicles, if it’s not a Ford and there are no aluminum valve stems, the system may be the indirect type (ABS wheel speed sensor-based). Look at the instrument panel cluster (IPC) to determine if the vehicle even has a tire pressure monitoring system. When you turn on the ignition, check for an amber low tire pressure light. Typically, if the vehicle is a deluxe model such as a GMC Denali, it will be able to communicate to the driver which tire is low. If the vehicle is a basic model, the driver will see only the icon on the IPC indicating that one or more tires are underinflated.

Always look at the displays on the dash or console (upper and lower) for a TPMS light or message during the first minute of driving. A TPMS light that stays on steady indicates a tire with low pressure. A flashing light indicates a problem with a sensor or the system. The flashing may last only one minute, then go back to a steady light, and will repeat at each ignition cycle. Keep in mind that a blinking TPMS indicator light does not always indicate a fault. Some will blink when the sensors are in sensor training or learn mode.

TPMS ECUs

Okay, so I’ve got a sensor that can detect a leaky tire and a display that tells my customer that either a tire is low (light on steady) or the system has a problem (light blinks for the first minute or so of each key cycle). How does all this connect together and work? Basically, TPMS sensors in the wheels send radio signals to a TPMS ECU, which, if there’s an underinflation issue, then signals the cluster to turn on the warning light. A more specific answer varies with each manufacturer. GM actually has one of the simplest systems. The TPMS sensors send radio signals with information that includes an ID unique for each sensor, and the radio signals are picked up by an ECU. The same ECU is also used to receive radio signals for the vehicle’s keyless entry system. The Remote Keyless Entry (RKE)—or Remote Function Actuator (RFA), in GM lingo—sees each sensor’s unique radio ESN and sends that data via the GMLAN (CAN) single- wire low-speed data bus to the instrument cluster to turn on a TPMS warning light.

At the other end of the scale, Chrysler has some systems that take a far more complex approach. The 2006 Grand Cherokee, for example, has three “middlemen” between the four TPMS sensors and the main tire pressure ECU. These middleman ECUs are transponders at three out of the four wheel wells—left front, right front and right rear. These modules receive the shortrange radio signal from the TPMS sensors located inside all four wheels, then communicate info like tire pressure and sensor ESN via a single-wire LIN data bus that’s connected to a wireless control module (WCM).

Only three middleman transponders are needed. The strategy goes like this: If signals from three out of four TPMS sensors are received and identified, the fourth signal must be the left rear wheel. The WCM in the Grand Cherokee’s case is the keyless entry/theft deterrent module, which Chrysler calls the sentry key remote entry electronic module (SKREEM). The SKREEM is the module that surrounds the ignition key lock cylinder and now is the main TPMS ECU as well. The module then puts the TPMS info on a CAN B two-wire medium-speed data bus to be monitored by the IPC/DIC, so the driver will know that a tire is low. Sound like a complicated system just to turn on a low tire pressure light? Yes, but no more so than many body electronics systems that use multiple networks to do a simple task like activating a trunk release.

New Sensors and Tire Rotations

Extinguishing a steady low tire pressure light typically requires put ting air in the tire (of course) and a little driving. Toyotas have a button (photo 3) to reset the tires after correcting an air pressure problem. Servicing these systems beyond adjusting air pressure, installing sensors in the wheels or doing tire rotations is a task for the above average tech who’s willing to make the investment in training and tools. Tire rotations are simple if the system is the basic version with a warning light and not an enhanced system with a message display that tells the driver which tire is
low. Just rotate the tires as usual.

If a vehicle with an enhanced system comes into your shop, your work will be a little more challenging. The ECU will think the left rear is still the left front, and so on. To prevent customer confusion and comebacks after a tire rotation, you’ll need to put the sensors into the learn (training) mode. This is where it can start to get fun. Just like everything else I’ve mentioned so far that varies from one OEM to the next, learn mode procedures are no exception.

On some GM models, you have to push the brake pedal and turn the headlamp switch off and on repeatedly. On some Fords, it’s a combination of brake pedal activation and the correct sequence of ignition cycling. Some GM models have driver info center prompts as you press buttons on the IPC. Some Toyota SUVs even have a second tire set switch in the glove box for the driver to select a totally different set of tires (winter, offroad, etc.) to install and introduce to the ECU. Swap the tires, press the button and a second set of sensors is already registered with the vehicle’s TPMS ECU to eliminate the need to run a completely new TPMS sensor registration/relearn procedure. Some vehicles must be driven above 15 mph for up to 10 minutes as part of the relearn procedure, while others, like Toyota, require a factory scan tool.

All the factory service info websites and most aftermarket service information sites cover TPMSs very thoroughly. Some TPMS tool manufacturers even include a printed manual with information on how each system works and how to handle extinguishing the TPMS light.

Electronic Tools: Wake Up & Talk to Me

Performing the learning function first requires that the sensors be awake and active. Some TPMS sensors need only a magnet to “ping” them into waking up in preparation for ECU learning. Every TPMS tool I’ve seen had one of these magnets (photo 4) in the kit with the electronic tool. After looking up the procedure for a vehicle on how to put the ECU into learn mode, simply place the magnet next to or around the valve stem (not Ford banded models) and the sensor will wake up and send out a signal for the ECU to interpret. On most models, when the procedure is completed for each wheel you’ll hear the horn honk, signaling it’s time to go to the next wheel.

Be aware that most systems don’t allow a lot of time to get the procedure completed. This means that on some models, if there’s a spare tire equipped with a TPMS sensor, you’ll need to gain access to it first before performing the learn procedure. Do your reading before doing the procedure. More often than not on newer systems, the sensors require some sort of electronic signal.

Some of the less expensive tools on the market do a “hunting” procedure that pings both frequencies of sensors that are in production as well as run various LF (Low Frequency – 125kHz continuous wave) and RF (Radio Frequency that’s pulse modulated) to wake up the sensor. These are the tools that typically have no display—only a few buttons and LEDs. Low cost and simplicity are advantages, but the disadvantage with some of these basic testers is that they won’t allow you to connect to a PC to download sensor information and they won’t show you the sensor’s electronic ID or read out pressure/temperature and battery condition if applicable. Full-featured testers (such as the two shown in photo 5) have menu-driven displays that allow you to scroll through a list of vehicles and select the vehicle/sensor type that pertains to that car, then sends enough of the right energy to ping the wheel you’re testing.

When using a TPMS tool, place the tool’s head or antenna against the sidewall of the tire next to the valve stem. The sensor signals won’t travel through metal. On banded-type sensors used on Ford (rubber valve stem), place the tester up to the sidewall 180° away from the valve stem, which is where the TPMS sensor should be. If you run into a sensor that does not respond when activated by the tool, try activating another sensor. This will help you determine if the tool is able to activate the sensor or if you have a problem with that particular sensor. Bartec offers a TPMS tool that not only activates sensors but can work with the vehicles in need of a factory scan tool to put the ECU into learn mode. It comes with a cable and connector for the OBD II style DLC (photo 6).

Keep in mind that checking for a bad TPMS sensor or prepping the sensors for a relearn are all these tools do. If the dashboard light is blinking due to a problem with the ECU, a serial bus problem or a bad transponder (Chrysler), you’ll still need a scan tool that can look at TPMS trouble codes and PIDs to diagnose the rest of the system. This is the same as any other electronic system on the vehicle.

Mechanical Tools & Spare Parts

The valve cores inside TPMS sensor stems are nickel plated to prevent corrosion. Putting the old-style brass valve core into the newer aluminum TPMS sensor stem is a no-no. After the dissimilar metals cause corrosion, the tire will begin to leak, not to mention the difficult time you’ll have removing the valve stem core down the road for tire service or replacement. Remember, a valve stem replacement is now anywhere from $25 to $150 or more instead of a couple of bucks, due to the TPMS sensor incorporated into the valve stem.

Also related to aluminum TPMS valve stems and the potential for corrosion and/or leakage is the valve stem cap. Those fancy chrome caps stand a good chance of corroding and seizing on the aluminum stem. Use only plastic or nickel-plated caps. A true TPMS valve stem cap will have a rubber seal in the top to seal out moisture. Don’t worry; customizers are already coming out with really cool valve caps that are compatible with TPMS valve stems.

Being kind to TPMS sensors and valve stems includes heeding the amount of torque that’s applied to the valve stem core. We’ve never had to worry about this before, but now we must protect those expensive sensors. The stem torque tool I use looks like a screwdriver handle with a valve stem core tool end on the bottom. You can’t tell by looking at it but it’s a torque wrench; once you hit a safe torque level, the tool makes the familiar torque wrench clicking sound.

Also, check the specs on the 11mm nut that holds the TPMS sensor in the wheel and torque it in place with an inch-pound torque wrench. Whenever a TPMS sensor is removed, always use new hardware when reinstalling either the old unit or a new sensor. The seal, threaded nut and associated metal washers come in inexpensive packages that are available from most parts stores either individually or as part of a kit that’s worth considering as a part of your shop’s TPMS arsenal (photo 7). Most manufacturers stress not reusing hardware, as the seals can have a memory that doesn’t allow alignment on reinstallation, causing a leak and an illuminated TPMS warning light down the road.

No doubt we’ll continue to see an abundance of sensors broken as techs learn hard (and expensive) lessons on how to mount and dismount tires with TPMS sensors. Most of the TPMS tool companies and the Tire Industry Association (www.tireindustry.org) have plenty of training available on these systems, including how to mount tires in a way that’s gentle to TPMS sensors. Common errors are breaking the bead right on the valve stem/sensor and not being careful with the sensor as you run the dismounting procedure. There’s a simple and inexpensive tool that suspends the TPMS sensor down into a safer area of the wheel as the machine does the dismounting (photo 8). A tip for mounting new tires: Grab your TPMS tool and ping the sensors as soon as the vehicle shows up at your shop. If three out of four wheels respond but the fourth does not, you can quote the customer a price for a new sensor before you get blamed for breaking it!

Costs & Future Concerns

All these new parts and processes can add up to some costly repairs. Some shops are already going overboard. I recently heard about an owner of a TPMS-equipped vehicle who priced a new set of tires and was told he’d have to see his dealer for new sensors. The dealer then told him it would cost $100 per sensor and another $200 to install and program. Yipes! What about a simple flat tire? Can it really cost $120 to fix a flat? A friend of mine who’s an avid fisherman in Florida recently found himself out that much after saltwater accumulated in his Toyota Highlander’s TPMS sensor valve stem during frequent boat launches, causing valve stem corrosion.

High vehicle mileage will take us on new adventures as we service these systems. We’ve all seen collapsed brake hoses and calipers that hold the pads on, making rotors glow red, pads wear out super fast and valve stem caps melt. What could that kind of heat do to a TPMS sensor? No doubt we’ll see all kinds of new twists to old problems with TPMSs as these vehicles rack up the miles. So as these systems keep evolving, we’ll all have to keep learning the latest tire pressure monitoring system service procedures.

Originally printed by Motor Magazine January 2009. link

About the author:

Dave Hobbs

For 20 years Dave Hobbs has been a hotline adviser, field engineer and technical trainer for a major automotive parts supplier where he has assisted thousands of dealer and independent techs with diagnostic problems. An ASE Master L1 technician, sponsoring member of IATN, MACS and SAE, Dave spent over 15 years as an independent repair shop technician prior to joining the OEM world. Visit Dave’s website at www.hobbsautotech.com

Check out some of the training videos featuring Dave Hobbs at www.auto-video.com.

By Dave Hobbs. “Hybrid vehicle electronics are dangerous and only the dealerships will be able work on them.” “The independent garage is on its way out.” Have you heard statements like these before? I have, and I have to disagree with these opinions, based in part on history.Let’s turn back the clock for a moment. It’s the 1960s and generators are replaced with alternators. A gloomy future is predicted for independent repair shops. My dad, Ray Hobbs, is working as an outside sales rep for a local auto parts store. He becomes quite successful selling alternator and battery testers to his independent repair shop customers. He has to learn the technology to train the mechanics to use the testers and ends up starting his own independent repair shop.

Soon after that, electronics appeared in charging and ignition systems in the 1970s. Then, in the ’80s, computers appear on all GM passenger cars and a sure demise is forecast for independent repair shops. By the late ’80s, computers and fuel injection are the mainstays. Mechanics step up to the plate, learn a minimum amount of electronics, purchase scan tools and DVOMs and earn the more respectful title of technician.

Then came the 1990s, with serial data buses linking the increasing electronic content together. Again, a gloomy picture is painted for the small repair shop. Finally, the new millennium is here, along with more electronics needing to be programmed with factory scan tools and factory Web-accessed calibrations. The aftermarket service industry hangs in there and learns about J2534 reprogramming tools.

So here it’s 2008, and more than a million hybrid vehicles travel our highways, with some now over eight years old and in need of service. A dismal future once again is predicted by some for independent repair shops. Is it true that hybrid vehicles can injure or kill you, or at the very least intimidate you with the “techno-shock” of increased complexity? There are now mysterious new systems never before seen on an automobile and suddenly it’s like 1981 all over again. But, as happened in 1981, I believe independent shops will adjust and move forward.

The Perfect Storm

To be fair to the predictors of doom and gloom, we’re facing what might indeed be a so-called perfect storm of technoshock in the aftermarket repair industry. This perfect storm is a combination of mega electronics content, high-voltage systems and ultra expensive components. For example, a DC-to-AC inverter on a new Chevy Tahoe hybrid retails for $1440. A few wrong decisions in your service bay and you’re either dead, in the hospital or at the very least explaining why the repair order has $5000 worth of parts on it.

Exaggeration, you say? Did you know that there are over 50 electronic modules on a new Tahoe hybrid? There’s plenty of techno-shock on other models as well. Check out the expensive-looking hardware under the hood of the latemodel Lexus hybrid in the photo at the top left of page 74. Do you remember the last time you replaced an electronic component that wasn’t actually bad? We’ve all done it. We try to stay up-to-date and have the proper equipment, training and information, but it still happens. Sometimes it’s the equipment’s fault, other times it’s the manual’s fault. Even factory online manuals can lead us down the wrong path at times.

I was working on a new hybrid vehicle with a no-start condition recently. Guess what I did for three hours? Follow the factory manual until I was blue in the face. I finally got the answer from another tech who had more experience on that particular vehicle model. I’m glad I hadn’t started replacing parts yet. It was simply a high-voltage interlock circuit that had been pinched in an accident. I repaired the wire and the vehicle started. More often than not, the lack of a rocksolid foundation in basic electronics skills is the cause for replacing good parts unnecessarily. The way to avoid that perfect storm of repair disasters is good, old fashioned basic electronics training.

Strugglers Everywhere

I’m both amazed and proud of the wealth of knowledge possessed by many automotive repair technicians. I’m also equally amazed by how many technicians are lacking in basic electronics knowledge—the simple things like understanding series and parallel circuits and knowing exactly what this thing called continuity is.

I was teaching a class on serial data buses not long ago to a room full of ASE master techs. I thought we were running along pretty well, with everyone on the same page. I began discussing the two resistors wired in parallel between the two high-speed CAN bus wires used to aid in high-speed data transmission. These two 120-ohm resistors in parallel can be checked for resistance by measuring between pins 6 and 14 at the DLC (see Fig. 1). On some GM SUVs and pickups, one of those resistors is located in a module, the other in the wiring harness above the fuel tank. You can imagine what happens in a humid or salty environment. When one of those resistors doesn’t have a good connection, there can be problems with bus communications. No problem: Just throw an ohmmeter between those two pins and take a reading.

I asked the class what the ohmmeter should read. When only two techs knew the correct answer (60 ohms), I initially assumed they were just bogged down by the high-tech nature of the subject of multiplexing. So I moved to the other side of the whiteboard and drew a pair of turn signal bulbs in parallel—a good, down-to-earth comparison, I thought. Everyone knows what happens to resistance when you add more light bulbs (resistances) in parallel, right? Apparently not.

I came to the conclusion that a basic foundation in electronics eludes many of us who otherwise can do amazing things under the hood of a car. It’s not just techs who can struggle; those of us who teach techs can struggle, too. That revelation came more recently at an advanced hybrid training class. I was in a group of techs who were all ASE Master L1 certified. We were working on a late-model Honda Civic hybrid with a classroom-induced problem. None of us had fewer than 15 years of hands-on wrenching experience and all of us had become teachers for either colleges or factory training programs. We were following the factory manual when it prompted us to use a meter to check for continuity to ground on a particular circuit. One of the instructors connected his red ohmmeter lead to the circuit being tested and the black lead to chassis ground. The reading was 4.62 megohms (see photo below)—as in mega, for one million. Can you believe we had a split jury on whether there was continuity? Two master tech/instructors said, “Yes, there is continuity,” while the other two said “No, 4 megohms is not continuity.” Yipes!

Training Revival?

If you aren’t nodding your head and saying Amen! as you read this, you may be a candidate for some basic electronics training yourself. Forget about serial data buses for the moment. Forget about multitrace lab scopes. Get some basic electronics training right now!

There’s more information out there than time to learn it. Some information on electronics is essential, some just nice to know. While experts agree that the fundamentals are where we need to begin, the same experts often don’t all agree on the methods. I hear instructors, shop owners and seasoned techs differ on the matter of how to get today’s typical technician to understand electronics. Electron flow or conventional flow? Atomic theory (electrons, protons, neutrons, etc.) or maybe we should just compare current flow to something simpler? Then exactly what simpler analogy do we use? Water in a hose? Hydraulics in a pipe? BBs in a tube? There are many methods being practiced.

Which method is best? What’s the best way to learn a new language or master a musical instrument or mathematical concept? The one that works for you! The water, hydraulics and BBs analogies all make sense to me because I already have a grasp of electronics. You may want to try them all until you find one that clicks in your head.

Considering the rise in popularity of hybrids, we must know what conductors and insulators are, for safety’s sake; knowing the number of free electrons in a certain conductor is less than essential. The following topics are considered by most to be essential information in your quest for mastery of basic electronics.

Ohm’s Law. Ohm’s law is an essential item to master. Within Ohm’s law is the knowledge of how volts, amps and ohms interact within both series and parallel circuits (see Fig. 2). Remember those CAN serial bus resistors being just like turn lights in parallel? The more resistors you connect in parallel, the lower the total resistance. Put the resistors in series and now you’ve got a higher resistance value for the total circuit. This concept should become as instinctive as riding a bicycle if you plan to avoid that perfect storm of techno-shock that’s coming your way. When you have Ohm’s law firmly in your head, you’ll be surprised how much you use it.

Here’s an example of Ohm’s law in action from a recent Trouble Shooter column. The problem involved a pair of injectors (wired in parallel) that cut out as soon as the engine started up. The tech discovered that if he disconnected the alternator, the problem didn’t occur. When the alternator is charging, the voltage applied to the injectors (and everything else) is 14.5 volts instead of 12.5 volts. That means the current will be higher (amps equals volts divided by ohms).

A failing injector can have a little less resistance in its winding than it should—for example, 1 ohm instead of 2 ohms. The higher voltage can push the ECM’s current limit over the edge and cause the two injectors to shut down when this occurs. The slightly higher voltage with the alternator charging was not the cause of the injectors cutting out but rather what pushed the ECM over the edge trying to drive a partially shorted injector. That’s just one practical and profitable application of Ohm’s law.

Abbreviations. You must know your abbreviations and definitions. Continuity (remember those instructors and their 4-megohms argument?), open circuits, short circuits, partial shorts, etc., are all essentials to master. Capital M stands for million, lowercase m stands for milli, or one-thousandth, and k stands for kilo, or 1000. These are extremely important concepts. You’d be surprised how many of us don’t know these, or have forgotten. You don’t want to mess up on this if you’re measuring a contact at the end of one of those high-voltage orange cables on a hybrid. Be safe by wearing Class 0 insulating rubber gloves (see photo), and make sure your meter is on the proper setting for the potential voltage range.

Meter Knowledge. How well do you know your meter? Does it feature auto ranging or manual ranging? Does it have a fused or unfused ammeter? Does it have and can you use the Min/Max and Averaging feature? Can you use and properly interpret Hz and duty cycle? If you’ve got a hybrid in your bay, is your meter CAT III? Are the leads and alligator clips/probes CAT III-certified?

Circuit Testing. Do you know what open-circuit voltage is? For example, what should the voltage on the PCM’s switched ground side of a fuel injector be with the key on, engine off? If you said battery voltage, great! If you said zero volts, you’re incorrect but in good company. This simple concept confuses many techs. When you get it straight, you’ll find it a timesaver when trying to determine, with one single probe of your meter lead, if a relay or fuel injector winding has a power supply, good winding/coil and if it’s turned on or shorted.

Do you really know when to use an ohmmeter and when to use a voltage drop test? This is sometimes debated even among experts. Most agree that a voltage drop test is the best way to test a circuit for good connection/continuity. An ohmmeter puts out a tiny amount of current and does its own voltage drop test, so to speak. Sometimes that tiny amount of current is not enough to cause an intermittent connection problem to break down. Putting current through the circuit as is done in a voltage drop test often will cause the bad connection to act up, leading you to a proper diagnosis.

My personal belief is that a voltage drop test is preferred hands down over an ohms test, but I still use an ohmmeter to test for a complete circuit, as a backup. If the load device is nonoperational or simply switched off, there will, of course, be zero current flowing. This means there will be no voltage drop. The ideal circuit’s voltage drop is small—.5 volt or less per connection.

Unless you connect a power source, ground and your own load to the circuit you’re testing, a voltage drop test can be misleading. If you’re using an ohmmeter as a backup test like I do, remember, the ground of the vehicle carries current, too. Every electron that goes through those red or pink 12-volt wires returns to the battery on black wires or the metal chassis ground. The ground is never dead when current is flowing somewhere on the vehicle. The ohmmeter must be connected to a dead circuit. It will show erroneous readings if connected to a live circuit. Something as small as a dome light switched on can mislead you in an ohms test on a ground circuit. Disconnecting the battery cable before using an ohmmeter is the best practice. Learn to do these tests with 100% accuracy and you’ll be years ahead of many of your competitors.

Where do you stand on basic circuit testing? Do you understand how a voltage divider network works? It’s tough to fix steering wheel controls without this knowledge. Most ABS wheel speed sensors and many engine control sensors also are involved with these voltage divider networks. In a nutshell, power (12 volts or 5 volts) is applied to one end of these series circuits and ground to the other. In the middle are two resistors. One resistor is a fixed value and is located in an electronic module connected to the circuit. The other is in series and varies with temperature or some other variable, or it could have a fixed value. The electronic module basically does a voltage drop test across its own fixed-value resistor to tell what voltage the other resistor is dropping. By doing this, the module knows things like what the engine coolant or air temperature is or if the knock sensor or ABS wheel speed sensor is disconnected.

Components. Do you know how basic electronic components work? Diodes, transistors, relays, resistors, capacitors, fuses, circuit breakers, fusible links and switches are everywhere. While you might never have to solder in a new transistor in your service bay, understanding what one does is important when you read a schematic. GM and Kia both use a transistor inside their ECMs to add or take away a pull-up resistor in series with the ECT. Taking this extra resistor out of the picture when the engine gets warm allows for better accuracy when measuring engine coolant temperature. Backprobe the ECT sensor when the ECM makes this change and you may mistakenly assume the ECM is bad (Fig. 3).

Sensors. Do you really know how sensors work? There are many types, including thermistors, potentiometers, Hall effect sensors, magnetic sensors, optical sensors, etc. Did you know that the two-wire ABS wheel speed sensor on some late-model GM vehicles produces a square wave? They’ve switched from two-wire magnetic sensors to a Hall effect style that doesn’t have a wire for a ground.

Are You Prepared to Weather the Storm?

Are you ready for future electronics subjects? Hybrid vehicles not only bring us high voltage but also three-phase AC. Terms like inductive reactance and capacitive reactance are coming your way, along with such components as contactors, HV (high-voltage) interlock circuits, IGBT drivers, inverters, converters, ultra capacitors and brushless AC induction motors. Better catch up with the electronics that are out there now so you’ll be ready to understand newer electronics training associated with these eco-friendly technological wonders.

This article is meant to stress the need for basic foundational electronics know-how. If you’re not where you’d like to be in the field of automotive electronics, find out where you can go for training. Hands-on training works best for most of us in the trade. You can expect to pay more for hands-on courses, but you can also expect to learn and retain more. It’s very important to find a training provider/instructor who can speak to you on your level. Some techs thrive on lots of information thrown at them in a short time, while others say slow it down a bit. When you find a training provider/instructor who works for you, stick with him.

Whatever method you choose and wherever you go for electronics training, remember to start soon. Make it your goal for next year. If you achieve that goal you’ll be on your way to surviving the perfect storm of new vehicle electronics that surely is coming your way!

Originally printed by Motor Magazine September 2009. link

About the author:

Dave Hobbs

For 20 years Dave Hobbs has been a hotline adviser, field engineer and technical trainer for a major automotive parts supplier where he has assisted thousands of dealer and independent techs with diagnostic problems. An ASE Master L1 technician, sponsoring member of IATN, MACS and SAE, Dave spent over 15 years as an independent repair shop technician prior to joining the OEM world. Visit Dave’s website at www.hobbsautotech.com

Check out some of the training videos featuring Dave Hobbs at www.auto-video.com.

By Dave Hobbs. Powertrain engineers continue to extract more power from and reduce emissions on conventional internal combustion engines. When both intake and exhaust camshafts get involved, GM’s variable valve timing system meets both goals.
Remember the good old days? Chubby Checker was singing “The Twist” and we had cheap gas and fast cars. I was a young mechanic a decade later, in the ’70s, and I can still re- call hearing my first GM muscle car sporting a performance camshaft loping into my bay. It was the sound of power, and I knew that this engine wasn’t going to the run like the rest!

With time comes change. Some 30 years later the stock engines of today can almost deliver the muscle car feel of yesterday, with hydraulics making camshafts to do “the twist.” Japanese cars have been doing tricks with cams and valves for years, but GM vehicles joined the variable valve timing game only in the last few model years. Now
they’re coming out of warranty and in- to your shop.

Twisting pretty much describes what GM is doing with its camshafts today. Valve timing improvements used to be accomplished via camshaft lift, duration and lobe separation. Those values were set in stone once the en- gine was assembled and were strictly the province of engine designers and performance enthusiasts. Not so with variable cam timing.

In 2002, GM released its DOHC in- line Six 4.2L engine, starting a new gen- eration of engines with variable cam timing. Given the term cam phasing by Delphi, the company that developed and manufactures the system, the en- gine first appeared in S/T model SUVs such as the Chevy TrailBlazer.
Several recent Delphi innovations such as flat-response knock sensors, electronically controlled viscous clutch cooling fans and throttle-by-wire—also made their way into this new power- plant. But in my opinion, the most no- table was the cam phaser. Attached to the sprocket on the exhaust camshaft, this device helps increase overall pow- er, improve throttle response and at the same time reduce emissions. Those goals are tough to accomplish simultaneously, but in this case they were, as a result of changing the rela- tionship between the camshaft and crankshaft to match engine power de- mands and conditions.

How Cam Phasers Work

The exhaust camshaft is bolted to a spe- cial timing chain sprocket that can run in lock step with the cam or retard up to 25° of cam angle (50° of crankshaft an- gle) when conditions warrant late ex- haust valve closure (see Fig. 1 on page 36). The swivel action of the cam phaser, which is identified in the service manual as a camshaft position actuator, is accomplished via oil pressure applied by an oil control solenoid into the actua- tor’s piston located in the hub of the camshaft sprocket. The sprocket’s inter- nal hub (the piston) and the end of the camshaft are helically splined together. A spring holds the piston forward (no retard), while applied oil pressure drives the piston rearward, retarding the ex- haust camshaft position based on rpm, crank position and cam position, along with TPS, MAP and BARO input val- ues to the PCM.

In 2005, GM switched to a newly de- signed actuator for the 4.2. It uses a four-vane actuator to control camshaft retard and advance. Inside the vane- style actuator assembly are a rotor and stator that are not mechanically linked together, as in the splined actuator (left photo at the bottom of page 36). In- stead, oil pressure is controlled on both sides of the vanes of the rotor, giving a hydraulic link to the stator. Varying the balance of oil pressure on each side of the vanes is how the cam is phased.

A return spring sits under the reluc- tor of the actuator to help keep it at a 0° (home) position. The actuator con- tains two cavities for oil to flow into— one for retard and the other for ad- vance. The electric oil control valve (OCV) controls which cavity receives pressurized motor oil (right photo on page 36). When the engine shuts down, so does the feed to the solenoid, allowing the actuator to move to the fully advanced position, locking a pin and ready for the next engine start.

Both the older spline-style and newer vane-style actuators use remotely mounted, 128Hz, pulse width modulat- ed (PWM), 10-ohm, four-way solenoids (usually mounted in the front of the cylinder head). Newer vane-style actua- tors are coupled with an electromagnet- ic coil situated on the oil control valve, which mounts directly on the front of the camshaft. On this style you’ll see the cam at the home position (0% PWM) or fully twisted to the opposite position (100% PWM) and averaging around 45% to hold the cam in place at the de- sired phase of retard or advance.

Why Cam Actuators Are Used

As important as understanding how these cam actuators work is understand- ing the reason behind using them. It’s all about valve overlap. Designers of performance engines often use valve overlap in a manner that allows the in- take valve to open while the piston moves upward on the exhaust cycle. A draft at the intake valve creates a flow of intake air to scavenge the cylinder for the following intake cycle.

GM, however, phases exhaust cam- shafts for a different reason: internal ex- haust gas recirculation (EGR). Internal EGR is accomplished by overlapping the exhaust cycle into the intake cycle. Think of the basic four cycles, then
imagine if the exhaust valve delayed closing well into the downward stroke of the intake cycle. The opposite of cylinder scavenging would take place. The movement of fresh air and fuel be- ing pulled down into the cylinder would create a draft to pull some of the ex- haust gases back into the cylinder.

Exhaust gas recirculation, termed by powertrain engineers as charge dilution, has been doing the business of NOX re- duction indeed for a long time. NOX, or oxides of nitrogen, is a compound creat- ed when nitrogen (N2) and oxygen (O2) combine at extremely high tempera- tures (2400°F and above). The primary factors that promote NOX formation in- clude temperature, time at temperature and the concentration of O2. These con- ditions usually occur when the air/fuel ratio is leaner than 14.7:1 for most nondirect injection gas engines. Oddly enough, when the air/fuel ratio goes past 18:1, the temps head back down and NOX formation is reduced.

The problem with external EGR as we know it is the nature of how the ex- haust goes back into the engine. EGR valves are in one location external to the cylinder, so whether they sit on the intake manifold or on a pipe that runs to the intake manifold, one or more of the cylinders are going to get too much EGR in order for the other cylinders to get enough. This unequal EGR distribution has plagued power- train engineers for years.

Internal EGR accomplished via ex- haust cam phasing is more effective. If the camshaft is twisted to a retarded position, with a cam actuator delaying exhaust valve closure by a few degrees while the intake stroke occurs, each cylinder gets an equal amount of EGR. Conventional external EGR has also been associated with engine pumping loses, which plague volumetric effi- ciency. In addition, internal EGR per- forms NOX-reducing charge dilution without increasing hydrocarbons (HCs). In a nutshell, internal EGR im- proves performance while reducing emissions, and that’s something every- one can be happy with.

Would the Intake Cam Like to Twist?

Starting in 2005, on twin-cam 3.6L V6 engines used in such models as the Buick Allure, Chevy Malibu, Cadillac CTS and Pontiac G8, GM moved its at- tention to phasing the intake camshafts as well as the exhaust camshafts. Whereas the primary benefits of ex- haust cam phasing are reduced emis- sions and greater fuel economy, intake cam phasing provides increased low- end torque and high-end power. In- stead of moving the intake cam to effect overlap in the exhaust stroke (cylinder scavenging), intake closure is delayed at the bottom of the intake stroke.

At lower speeds, an open intake valve during the first few degrees of compres- sion often results in air being pushed back out the intake valve as the piston moves upward. At higher speeds this is- n’t a problem, and the intake valve that lingers open into the compression stroke allows the air that’s been moving into the cylinder to keep coming in un- der the momentum the air charge has acquired. The result is a cylinder with greater volumetric efficiency.

Overhead-cam engines that phase both intake and exhaust cams use a vane-type actuator. Pushrod engines, as of the 2007 model year, are no longer confined to the set-in-stone mode of cam timing, either. Look for full-size trucks, SUVs with V8s, along with Corvettes and the all-new 2010 Chevy Camaro to start appearing in your bays soon sporting variable cam timing on their single-cam-in-block engines. Us- ing a vane-style actuator, these engines differ from overhead-cam engines in that they push the oil control solenoid back into a hollow portion of the front of the camshaft. Four small oil holes are situated in the camshaft to line up with the oil control valve/solenoid. The elec- tromagnetic portion is also similar to vane-style actuators.

When Cams Don’t Do the Twist

In addition to the typical OBD II camshaft position sensor (CMP) codes, there are a new set of trouble codes to determine if the camshaft(s) moved to the correct position when commanded.

Supplementing those are DTCs that advise us if the actuator/oil control sole- noids are open or shorted. Testing these systems is quite easy if you have a scan tool with bidirectional capability for ad- vanced GM engine output functions. Simply idle the engine, go into the out- put controls function of the scanner and command the actuator to move the cam from its current position (see Figs. 2 and 3 above). You’ll know it has moved by the way the engine runs. It may even stall. PIDs relating to engine load, such as MAP sensor values, will indicate an engine that’s idling poorly. Cancel the cam timing command and the engine should go back to a nice idle.

If the engine is idling poorly and/or stalling when it comes to your shop and the cam timing control function of your scan tool has no effect, then you know the actuator is stuck or is not being sup- plied with oil due to a clogged oil pas- sageway or bad solenoid. The stories of poor oil change maintenance and its ef- fects on GM variable valve timing are common with both dealers and inde- pendent shops, so if your customer has a vehicle with one of these systems, you really should encourage him (more pas- sionately than usual) to adhere to the scheduled oil change intervals appropri- ate for his style of driving.

Besides the oil cleanliness issue, one pattern failure seems to be with the oil control solenoids on the earlier spline- style systems used on the 4200 L6. The two-wire electrical connector has a seal that leaks oil from within the solenoid. Pop off the connector and look for leak- age (see the photo and inset at left). If it leaks you’ll have to replace the solenoid, and that means pulling the power steer- ing pump out of the way to clear the cylinder head.

A word on R&R procedures is merit- ed here. To replace the actuator on the 4200 L6, you have to pull the intake, al- ternator and few other choice compo- nents just to get the cam cover off. About the time you get all of that done, it’s easy to get anxious and just remove the actuator from the front of the camshaft. Don’t! If you do, the timing chain tensioner will ratchet the chain down as you slide the actuator off. If you thought you had to do a lot of work to get this far, just wait until you start pulling the front cover off and find out you have to remove the oil pan. Removing the oil pan on 4WD models means pulling the halfshafts out of the pass- throughs in the oil pan. Better take your time and purchase or borrow a Kent- Moore J-4417 or equivalent (see the photo), a hooklike tool that holds tension on the chain, allowing you to re- move and replace the actuator without pulling the front cover.

Another tool I see some dealer techs using is a simple pitchfork-looking de- vice (such as the one shown in the bot- tom photo below) that goes through the gap between the chain and the front cover all the way down to the tensioner to keep it from pulling up when the actuator is removed. V6 models require a pair of long rods (such as the Kent-Moore EN-4813) with spreaders on the bottom to pre- vent the tensioner from flopping back as the actuator is removed.

As with any OHC timing chain service procedure, consult the service manual to determine how to properly line up the sprockets before taking anything off. When removing or installing the actuator on a cam-in-block V8, make sure you don’t push on the actua- tor’s reluctor wheel. It’s held together with three roll pins that could become dislodged, causing an internal spring to push the assembly apart in your hands.
This will create some extra grief at the least and an injury to your hands at worst. Do your pushing and pulling by the sprocket and once the actuator is off the engine, it’s a good idea to run a tie wrap through the hole where the camshaft goes around the entire sprock- et/actuator assembly to hold things in place prior to laying the actuator down on the bench.

On the subject of proper care for these actuators, GM has special TSBs called Preliminary Information bulletins (PIs) that are very helpful. PIs are typi- cally not available via aftermarket ser- vice information sources; you must have a subscription to ACDelco’s SI 2000 on- line information system to see them. Subscriptions are now available on a short-term basis for a modest fee, simi- lar to other OEM websites.

PI 00771 gives techs a good heads- up on proper cam actuator handling on inline 4200 6-cylinder engines. Prior to replacing the actuator on these en- gines, you’re supposed to turn the crankshaft several times until the name “Delphi” on the actuator’s face is on top and horizontal. When tightening up the bolt for the new actuator, many techs hold the actuator with slip-joint pliers, which is a recipe for a DTC and a comeback. Use a 1-in. wrench on the hex surface to hold the actuator and you’ll be fine. PI AIP3334 makes a slight correction to TSB 08-06-01-011 along similar lines on how to install an actuator on V6 models.

While these engines aren’t quite the muscle car powerplants from the good old days, variable cam timing, whether in a 2002 TrailBlazer L6 or a 2010 Camaro V8, brings GM a little closer to that mark while still maintaining good idle, reduced emissions and better fuel economy. For technicians in the field, a little knowl- edge, up-to-date service info and re- membering to stress to customers the need for proper oil change maintenance will allow engines with variable timed camshafts to keep “doing the twist” for years to come. Chubby Checker fans should be proud!

Originally printed by Motor Magazine August 2009. link

About the author:

Dave Hobbs

For 20 years Dave Hobbs has been a hotline adviser, field engineer and technical trainer for a major automotive parts supplier where he has assisted thousands of dealer and independent techs with diagnostic problems. An ASE Master L1 technician, sponsoring member of IATN, MACS and SAE, Dave spent over 15 years as an independent repair shop technician prior to joining the OEM world. Visit Dave’s website at www.hobbsautotech.com

Check out some of the training videos featuring Dave Hobbs at www.auto-video.com.

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Sometimes techs under think and just hook up their smoke machine to the evap test port and ‘let her rip’ (maybe closing the vent solenoid) and other techs over think by trying to use their scan tool to run all sorts of tests watching the tank pressure sensor while ignoring the smoke machine.  In this video clip, watch Dave explain the right combination of scan tool and smoke machine usage to find the source of your evap leak.