September 28, 2011
TPMS: the next generation
As tire pressure monitoring systems evolve, universal sensors are on the rise
By: Mike Mavrigian and Bob Bissler
A standard snap-in valve (left) next to a TPMS valve, which has a beveled base at the bottom of the threads and an air transfer stem.
They’re becoming a greater fact of life for tire dealers. Tire pressure monitoring systems (TPMS) have been required on all new vehicles under 10,000 pounds since 2007. But the technology was first required on 10% of vehicles in 2001. Now, some of those older sensors are reaching the end of their service life.
“Battery life for the very early versions was 3-5 years, and now the later versions are 5-7 years,” says Gary Luginbuhl, training manager at Myers Tire Supply. “We really don’t know how long they’ll last yet because nothing’s been out there that long. The early ones are starting to fail, the ones that were out there in 2001-2002.”
The pressure sensor transmitters (one transmitter mounted inside each wheel) monitor inflation data and send an FM radio signal to the system’s antenna and receiver, which then sends a digital signal to an electronic control unit (ECU).
Today, the TPMS (where actual tire inflation pressure is monitored) is referred to as a direct system. The system is calibrated to alert the driver when one or more tires have lost 20-25% of the programmed inflation pressure.
The basic three
Three basic “styles” of TPMS sensor/transmitters are available: banded, snap-in and clamp-on. Banded sensors are affixed to the inside of the wheel using both a positioning adhesive (peel off) and a large diameter worm-drive clamp (the wheel valve is the standard valve style that has been in use for decades). Both clamp-on and snap-in sensors feature the valve stem as an integral part of the sensor. A clamp-on sensor mounts via the wheel’s valve hole and is secured with a mounting nut. It is sealed with a separate grommet. The snap-in style features a traditionally mounted rubber valve style.
It’s important to quickly identify a snap-in style sensor. The valve stem caps are longer than a traditional stem cap, and (with the cap removed) you’ll notice a beveled brass surface at the base of the cap mating area.
Banded TPMS sensors are still found on some Fords. Other makes/models utilize clamp-on or snap-in sensor styles, where the valve is an integral part of the sensor. Another integral part of the sensor is the frequency in which it transmits.
“There are two different sensor frequencies for domestic and import: 434 megahertz is the import (foreign makes that are sold in this country); and 315 megahertz are the domestic, GM and Ford,” says Luginbuhl. “It’s not 100% because there are some Nissans that are 315 megahertz.”
There are several sources for OEM TPM systems: Schrader International, Borg Warner Beru Systems GmbH and Pacific Industrial Co. Ltd.
Schrader systems are found on Ford, Chrysler, GM and Nissan/Infiniti applications. Pacific systems are found on certain Lexus vehicles, and Beru systems are used on Mercedes-Benz, Porsche, BMW, Audi/VW and Land Rover models.
The majority of OE TPMS sensors are stem-mounted. The primary reason involves diagnostic capabilities. If the sensor is band-mounted and deeper inside the wheel, it’s more difficult for the signal to pass to the diagnostic tool, whether the system uses an RF signal or a magnetic signal.
Universal sensors to the rescue
“When you look at brake pads, starter motors, wiper blades, oil filters, exhaust systems and so on, the OEs never, ever standardized anything,” Luginbuhl explains. “They did the same thing with TPMS. What they ended up doing was creating a gridlock of technology and service support for the aftermarket dealers, our customers. The OEs went with multiple sensor manufacturers, multiple signal protocols and numerous shapes and styles of sensors to react to the mandate.”
Currently there are an estimated 75 versions of TPMS sensors in OE use. As a result, it’s impossible (or at least extremely impractical) for any shop to stock enough sensors to accommodate all makes/models/years.
“The big issue for the tire dealer has been that there are 75 of these on the market and they don’t know what kind of vehicle is going to pull into their shop,” says Luginbuhl. “You’ve got a minimum of four each and these are $50 to $150 each, so for a dealer to stock 75 different types – it’s not going to happen. The OEs took the good old universal rubber snap-in tire valve that we all grew up with, that you can snap into any vehicle anywhere, and they made the tire valve into a make-model-year specific device, just like a starter motor. That’s what the dealers have to deal with now.”
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