If you’ve done any tire and wheel installation in the last six years, you probably know quite a bit about TPMS – which became mandatory in 2007 on all passenger cars and light trucks thanks to the TREAD Act, signed into law in 2000. 
But one thing you may not know is how effective TPMS has been in the aggregate. According to NHTSA’s November 2012 TPMS Effectiveness Report:
• Safety studies have shown that the presence of TPMS resulted in a 55.6% reduction in the likelihood that the vehicle would have one or more severely underinflated tires.
• An estimated 250,000 vehicle crashes are caused by underinflated tires each year. Vehicles with properly inflated tires experience optimum ride and handling, shorter braking distances, longer tire life and improved fuel economy.
• Properly inflated tires save the typical passenger car 9.32 gallons of fuel, and over an entire year, TPMS saved some $511 million for the TPMS-equipped vehicle population.
But the clear advantages and efficiencies of TPMS don’t mean there haven’t been a lot of problems along the way. Many dealers and tire techs view TPMS as just one giant headache, or even the perfect example of the government trying to solve a problem by creating a catastrophe.
Six years into the great TPMS experiment, as first-generation sensors are beginning to reach the end of their useful lifetimes, it seems like a good time to take a look back and review the many problems involved in TPMS and take a look forward, as well, to see how those problems are being solved in the second generation of sensors.
One of the most frustrating initial problems installers encountered with TPMS was the incredibly wide variety of OEM sensor types, to the point that not only does just about every make of car use a different style of sensor, but it sometimes seems as if each car model carries a different sensor. Barry Steinberg, CEO of Direct Tire and Auto Service in Boston, notes, “It’s painful, it’s just painful. Every car has different sensors. BMW just changed to another sensor, so they’ve got, like, four different sensors now.”
Fortunately, in recent years, aftermarket companies such as Schrader, Dill Air Controls, Oro-Tek and many others have stepped up and provided programmable multi-vehicle sensors that can be used across make and model lines. Most dealers can now cover 80% to 90% of all vehicles while stocking only three or four sensor types.
Paul Wise, director of product management and marketing at Schrader, says, “With our patented EZ-sensor option, a service and repair facility can stock just two sensors (315 and 433 Mhz) and program them to over 85% of TPMS-equipped vehicles that they may see come into their shop. This eliminates the need to stock hundreds of the original replacement sensors.”
Sensor Damage and Corrosion
This is a good thing, because it turns out sensors need replacing quite a lot. Most OE sensors are extremely fragile, requiring tire techs to take great care when mounting or dismounting tires to avoid breaking the monitor off the valve stem. The best method to avoid damage to the stem usually involves removing the valve core to deflate the tire, then removing the nut that holds the valve stem to the wheel, thus allowing the stem and sensor to simply drop inside the tire to be retrieved after dismounting.
The second best technique is to ensure the tire-changing machine’s shovel is placed to break the bead at 180 degrees opposite the valve stem, so that neither the shovel nor the tire bead can put pressure on the sensor. Care must then be taken when the wheel goes onto the tire machine to place the valve stem at “11 o’clock” or just to the left of the mounting head, so that the tire bead does not contact the sensor when it moves downward into the wheel’s drop center.
By far, the most prevalent reason today for sensors needing replacement is simple corrosion. The metal valve stems on most first-gen OE sensors have shown a spectacular ability to corrode at the least provocation. Horror stories abound, even to the point of having stems snap off vehicles while in motion, leading to catastrophic pressure loss situations.
Sensor corrosion tends to be at its worst in high-salt areas, either near the ocean or where road salt is used during the winter, but most nickel-plated sensor stems will corrode in nearly any conditions. And some vehicle makers – we’re looking at you Chrysler/Dodge/Jeep – come up quite often in driver complaints about sensor corrosion.
Almost as bad has been the tendency for corroded stems to make it difficult or impossible for a technician to remove the retaining nut from the valve stem without damaging or destroying the stem. When the nut freezes to the stem due to corrosion, turning the nut will either snap the stem off entirely or cause the stem to turn instead of the nut.
A few first-gen sensors were built as two pieces so that a corroded or damaged stem can be removed from the much more expensive sensor, but most OE sensors are designed as one integrated piece, such that the stem cannot be removed from the sensor without destroying the entire assembly.
Nearly all aftermarket sensors are now a two-piece design with a snap-in rubber valve stem rather than the earlier one-piece designs with metal stems. This solves one of the most glaring design flaws involved in making a simple, inexpensive valve stem into a complex, expensive piece of electronics.
Additionally, the problem was made much worse by early sensors using metal valve caps that very quickly welded themselves to the stem. Steinberg says, “Initially, they were putting out a lot of metal caps on these metal valve stems and they were seizing and cracking and breaking. But ever since they’ve all gone to plastic valve caps, we’ve seen a lot less of that.”
The only real defense against corrosion is proper maintenance. This is why it is so important to employ the service packs on TPMS sensors every time the tires are serviced. Replacing the nut on the sensor stem often prevents corrosion from having enough time to take hold and weld the nut and stem together.
Replacing the rubber O-rings eliminates problems from dried out O-rings leaking air. Replacing the valve core also is necessary, as the nickel plating will wear off over time.
It’s also important to ensure all technicians who perform TPMS service know the inflexible rule of valve cores. Never ever put anything other than the proper nickel-plated valve core into a TPMS valve stem. Brass valve cores will galvanically weld themselves into the stem in a very short time, becoming impossible to remove. It can be just that easy to destroy an expensive sensor with a 50-cent mistake.
Battery Life Issues
The last major problem with first-generation sensors is still somewhat on the horizon, but coming quickly: batteries.
Battery life for TPMS sensors is generally projected to be in the range of six to eight years at best, which means that with major sensor use starting in 2007, you can expect to start seeing substantial battery failures starting about now, with a major wave of failures coming in the next two to three years and continuing into the next decade. Unfortunately, the vast majority of sensors were designed as sealed units and it is impossible to simply replace a battery.
So, in essence, you will need to be ready to replace a whole lot of sensors in the coming years, and, in general, your customers are not going to like hearing that. However, having the proper tools and equipment in place to make the process as easy and economical as possible will go a long way not only toward easing that blow for your customers, but decreasing the headache for your shop.
• Possibly the most useful tool you will need for TPMS is a good sensor scan tool. Actually, if you’ve been dealing with TPMS at all over the past six years you probably already have one, but now may be a very good time to look at upgrading to the newest model. Today’s scan tools not only perform the essential “test before touch” job to verify that sensors are working and perform sensor relearn and ODBC programming tasks, but also can print reports that will both show your customers what’s going on with their sensors and provide an audit trail, if necessary, to verify that you are following NHTSA regulations.
• It’s also best to have torque-protected hand tools designed to avoid over-torquing sensitive TPMS components like the nut and the rubber o-rings.
• Finally, of course, you will need to have a good stock of replacement sensors that fit your business and the needs of your customers. Keeping a smaller stock of programmable or multi-vehicle aftermarket sensors does seem to just make more business sense and will probably cost your customers quite a bit less than keeping hundreds of OE sensors to be able to cover every possibility, or having to search for just the right sensor when you need it.
So, in general, the second generation of TPMS seems to be maturing just in time for the first to step aside. It may even be that the automotive aftermarket really can manage to take a catastrophe and reduce it to a mere problem.
As Winston Churchill once said of the Allied invasion of North Africa, “Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.”
Here’s to the next generation.
