Tire pressure correct? Check. Tire balanced? Check. TPMS initialized? What?
Tire pressure monitoring systems (TPMS) have been in common use for several years now, yet when I asked the technical support specialists of several aftermarket companies what the most common request for help is, they told me two things. First, many of you are having problems updating or using their tools, and two, basic reset and relearn procedures are giving you fits. Because it is one of the major aims of Motor Age to make life in the shop easier on you, let's see what I can do to take care of at least the second problem in this month's feature.
Why TPMS?
Every tech who has held a wrench for even a little while knows that nearly every car that enters his or her shop has at least one tire that is underinflated. But did you realize that nearly 250,000 accidents and close to 800 fatalities every year can be attributed to underinflation? Underinflated tires run hotter than ones that are properly inflated and can lead to structural failure of the tire itself. They can lose their seating to the rim, which also can result in a catastrophic loss of air. Either scenario could result in loss of vehicle control.
A significant change that resulted from the passing of that act is the requirement that all vehicles sold in the United States with a gross vehicle weight rating of less than 10,000 pounds be equipped with a means to monitor the vehicle's tires and warn the driver when tire pressure in any of the tires dropped to an unsafe level.
I started in this business in a time when there still were neighborhood service stations (stress the word service). Back then, the attendant (you?) would put the gas in for the customer and while he was doing that, he'd clean the windows, check the fluids and correct the pressures in the tires. Whose doing that for your customers now? Exactly.
TPMS systems are required to warn the driver if tire pressure drops more than 25 percent below specification. Considering 10 percent under inflation can cause handling issues and greater operating temperatures, tell your customers that TPMS is not a replacement for routine pressure checks and show them how to do just that.
But TPMS does serve a worthwhile purpose. You should treat this system as importantly as you would any other safety related system, and teach your customers that the little yellow warning light glowing on their dash is not there to cause them inconvenience, but to help keep them and their families safe.
Everyday Information
TPMS is not a new concept, making its first appearance in 1986 on the Porsche 959. After the TREAD Act, OEMs began phasing in systems to meet the requirement that all models be so equipped by the 2008 model year. While there are variations in the types of TPMS systems you'll come across, there are a few general tidbits you should be aware of when servicing any of them.
First, does the vehicle even have TPMS? Models starting right around 2004 may or may not, and simply looking at the valve stem isn't going to tell you anything. The clue you should make a habit of looking for is the presence of the telltale yellow light on the instrument cluster as the IC goes through its Key On, Engine Off bulb check.
An important reason for making this check on every car is to avoid potential customer comebacks after performing a routine service like a tire repair or rotation. Many systems have to be retrained after a tire related service. If you don't, the light might not illuminate until the vehicle has exceeded a minimum speed. You know, right about the same speed your customer reaches just five minutes after he's left your shop. If the car comes in with a TPMS warning already stored, your customer might not have even noticed, but I guarantee he will as he leaves. Because you didn't catch it and tell him about it, you might find yourself on the hook for some expensive parts that were broken by someone else. That never happens, right?
Indirect TPMS
Early TPMS systems were indirect systems, utilizing the existing Antilock Braking System (ABS) sensors to monitor tire pressure. Underinflated tires are not as big around as those that are properly inflated, and the control module in charge typically monitors the tires in diagonally opposed pairs, plugging the information it receives into an algorithm incorporated into its programming. But this system has its drawbacks, one of which is the need to first tell the module what's normal.All indirect systems, regardless of manufacturer, have some type of initialization procedure that must be performed to make sure the control module has a proper baseline for future tests. Generically, this is performed first by correcting all of the tire pressures to specification and then placing the module in learn mode. The vehicle then is driven to give the control module the opportunity to learn what's correct. Road surface irregularities might suspend this learning process, as will problems with the ABS system itself.
Because this system monitors wheel speeds (in turn affected by the rolling circumference of each tire), mix matching tires on the same axle can trigger false warnings. This includes things like installing a single new tire opposite an older one, installing the spare, or even installing non-OEM approved tires.
Direct TPMS
Direct TPMS systems are dedicated systems that use sensor/transmitters in each tire. Sensors come in three designs: band-type sensors that use a metal band to secure the sensor to the center of the rim 180-degrees opposite of the valve stem, and two different stem designs. The older of the two uses a metal stem incorporated in the sensor assembly. The other uses a traditional looking rubber stem that attaches independently to the sensor, easily mistaken as a normal stem.
Domestics and Asians take a different approach to teaching their control modules what sensors are where. Think about it for a minute. These are little transmitters, and if each transmitted identically it wouldn't be long before we had issues with cars next to us at a stop light triggering our dash's warning lights. Each sensor has a unique identification that the control module needs to know before it will pay any attention.
Many Asian makes don't allow their control modules to learn these IDs on their own. Instead, they require a capable scan tool or TPMS tool to pass the IDs on. On these cars, IDs must be rewritten to the ECU anytime a sensor is replaced and often, even if the tires are simply rotated.
The process is relatively simple, though. If you're using just the scan tool, you might want to write down the IDs of any new sensors you are installing and in what wheel position they were returned. If you have one of the more capable TPMS tools in your shop, you can use it to read and record this information. Once that is done, it is simply a matter of connecting the tool to the control module via the Data Link Connector (DLC) and overwriting the information in the assigned control module.Here's a tip for you I learned from my tech rep buddies. Honda is one example of an Asian make that requires you to write the IDs of new sensors, and the process is straight forward enough. After you're done, though, the light is still on. Why? The car has to be driven over 28 mph after the rewrite before the system will reset, a relevant bit of information your service manual may or may not tell you. Go drive it around the block!
Domestics typically allow their modules to learn without outside assistance. On these, the vehicle is placed into learn mode and then the sensors are triggered in a specific order (usually starting left front and working around the vehicle clock-wise). Getting to learn mode on many models now involves the key fob, and a weak battery in the fob may just keep you from turning that TPMS light off. Triggering the sensors might require adding or bleeding air from the tire, using a magnet placed around the sensor stem, or by using a dedicated TPMS tool to trigger a sensor response.
A worthy note to remember here, even more so if you work for an OEM dealer: When learning the sensors, it is possible for another vehicle's sensor to be learned if it is close enough, compatible and awake. One technical rep even shared a story of a tech that had problems learning a system, only to find out that the car was trying to learn the old sensor he still had in his pocket!
Finding What You Need
As with any other modern automotive system, there is no "one size fits all" procedure for dealing with TPMS. Aftermarket service information systems are getting better at supplying what you need but locating it can often prove a challenge. Mitchell 1 publishes a guide that is an example of one source of TPMS service information neatly assembled in one manual all the techs in the shop can access. Bartec USA, a TPMS tool manufacturer, offers dedicated Internet based resources and tech support and its model 400 easily allows you to rewrite Asian IDs.
Snap-on's latest TPMS tool, the TPMS3, incorporates the procedure listings directly in the tool, also is capable of rewriting Asian IDs via the DLC, and is very user friendly. OTC takes a unique approach, striving to make the whole process standardized by incorporating its TPR tool into its Genisys scan tool. While the TPR tool can be used as a stand-alone device, when mated to the Genisys, the scan tool literally will walk you through the procedures with on-screen prompts. Join us online in the AutoPro Workshop (Workshop.Search-AutoParts.com) to see video of these different tools in action.
Later this month, Motor Age and TST will be hosting a free, live and interactive, webcast sponsored by Bartec USA. We'll focus on servicing TPMS and the new E-Z programmable sensor. For more information, or to register, log on to www.MotorAge.com/TPMS.
