Auto Service World
Feature   June 1, 2010   by Tom Venetis, Editor

TPMS Are Nothing to Get Nervous About

TPMS systems are here to stay and should be treated like any other maintenance item in a vehicle

It has been ten years since the TREAD Act in the United States established that vehicle makers needed to put in systems that would alert drivers if their tires registered 25 per cent or more tire under-inflation. The Act and the 25 per cent under-inflation target is meant to give drivers a greater margin of safety by preventing them from driving with under-inflated tires while also improving fuel economy by ensuring that tires remain properly inflated.

When TPMS systems soon appeared on new vehicles, the technology seemed to pose problems for independent technicians. While the TREAD ACT and subsequent legislation made the systems mandatory, no effort was made to put into place a single set of rules for how TPMS systems should operate. The result was each vehicle maker had a system that was different from another.

Bob Bignell, executive director of the Ontario tire Dealers Association says with all new vehicle technologies some technicians early on embraced TPMS as a new challenge while others cast a more skeptical eye, waiting to see how the technology would evolve.

“Today, you can’t avoid the technology,” says Bignell. “It has to be treated like any other maintenance item in a vehicle. It will fail and you will have to fix it.”

Bignell says it is important that technicians get proper training on how to handle TPMS technologies and to learn the right way to replace even seemingly simple things. With non-TPMS vehicles, changing or replacing tires and valve stems was something that was done easily. If a valve stem was broken it was not a problem, as traditional valve stems were a common and inexpensive part to replace.

Things are different now. Bignell says replacing a valve stem and grommet on new TPMS-equipped vehicles is a more complicated matter — and a much more expensive one as well. A common problem is for the stems to be broken by mistake or to be torqued in incorrectly, resulting in either breakage of the stem or galvanic corrosion setting in because of a mistaken torque pressure being used.

Then there are issues with the sensor themselves. Depending which sensors are used there are different torque requirements.

Sean MacKinnon, an instructor with the Tire Industry Association and someone who spent more than a decade in the tire retail industry, says technicians can make a mistake if they replace an OE sensor with another manufacturer’s sensor. A favorite example he likes to cite in his training sessions is the Chevrolet Cobalt 2009. This popular vehicle can use either a Continental Siemens or a Schrader OE snap-in sensor valve. Where a technician can make a mistake is both of these snap-in sensors need different amounts of torque so the sensor nut can be tightened to the wheel surface. If the technician has always used the Continental Siemens sensor he or she will know to use 80-inch pounds of torque. However, the Schrader sensor needs only 62-inch pounds of torque.

“So what often happens is the technicians torques the Schrader with 80-inch pounds of torque and breaks the sensor,” MacKinnon says. “So if that sensor is US$60 to buy, you have to do a lot of sales to make up for that loss.”

And there are other issues as well that can become a bit confusing. Every vehicle with a TPMS system has unique quirks during the re-lean after replacing the sensors. A technician can install new sensors on a vehicle, run through all the correct checks, but still have an indicator coming on saying there is a problem. On a Toyota Prius, when doing a tire rotation and replacement, it is key that the technician use a properly formatted scan tool when replacing sensors as the system needs the scan tool to properly learn the new sensor IDs. On a Honda Pilot, things get even trickier. A technician will have to drive the vehicle for 40 seconds at 15 miles-per-hour at the correct tire pressure in order for the vehicle’s onboard systems to relearn.

Because it can be difficult to keep up with all the different re-learns on vehicles, TIA -both in Canada and in the United States -has released a TPMS Relearn Chart which is updated every year. The chart provides a listing of all the relearns on both domestic and import vehicles, each broken down by make, model and year. It provides technicians with a re-learn summary, replacement part numbers and torque specifications.