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Spokane, Washington  Est. May 19, 1883
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Autos

Getting familiar with TPMS

Since 2008, vehicles have been equipped with Tire Pressure Monitoring Systems.  When things are okay, you don’t even know they’re there, but when the pressure in one or more tires drops by 25 percent, you are warned.

That warning will be an illuminated instrument cluster light that looks like an exclamation point within a tire’s cross-section.  If you have TPMS, you can identify the symbol, among others, when you turn the ignition key to “on” before starting the vehicle.

Manufacturers began installing the systems before the National Highway Traffic Safety Administration’s 2008 mandate.  Approximately 20 percent of new vehicles made from October 2005 through August 2006 are equipped with TPMS, along with 70 percent of those built from September 2006 through August 2007, and 100 percent of September 2007 and later production.  TPMS information is found in a vehicle’s owner’s manual.

Drivers who have TPMS on their vehicles should be aware of its presence and operation.  TPMS can provide surprises, as reader R.T noted, “I have a 2012 Highlander. I have 4 almost brand new mounted winter tires.  I took my Highlander into [a dealer] for the 5000 mile check and also to have the mounted tires installed.  I was told that because of the TPMS law they could not change the tires unless they installed the sensors in the wheels at over $100 per wheel plus tire work to install the sensors.  I could see at least $500 for this.  The service guy told me that no tire shop would put on my wheels because of the law!  I called two tire shops in Cda and they told me that they do mount tires without the sensors and it is legal.  They cannot do anything to disconnect the tire sensor system in the vehicle, that is what is against the law.  But [the dealer] did not tell me the whole story.”

The dealer R.T. encountered had a policy of not mounting tires/wheels without pressure sensors; they instead offered to mount sensors on his existing wheels that would work with his Highlander’s TPMS.

R.T.’s TPMS is a “direct” system, which is most prevalent.  VW and Audi use an “indirect” system, employing wheel speed sensors (part of anti-lock brake system).  One advantage of the indirect system is that there are no sensors in the wheels, so no special procedure is required for installing custom or winter wheels.

Direct systems use a special air valve containing a sensor, and have an elongated, sealing valve cap to protect the delicate innards.  The sensors communicate with a vehicle’s ECU (electrical control unit) using RF (radio frequency) signals.  R.T.’s dealer was right when they told him that sensors cost around a hundred dollars each.

But wheels without sensors CAN be legally mounted on vehicles with TPMS — the low-pressure warning system will simply be inoperable.  The federal law, 49 U.S.C. 30122(b), states, “A manufacturer, distributor, dealer or motor vehicle repair business may not knowingly make inoperative any part of a device or element of design installed on or in a motor vehicle or motor vehicle equipment in compliance with an applicable motor vehicle safety standard.”  Some shops evidently interpret the installation of wheels without sensors as violating the law, which is not the industry norm.

No one wants to hear of a $400-$500 hidden cost for mounting snow tires/wheels.  It is expected that sensors, which are self-contained and universal-fit, may see a price drop as progression in manufacturing technology and market saturation ensues.

The virtues of proper tire pressure are well established, to include tire life, handling, safety and fuel economy.  For me, a self-admitted maintenance fanatic who regularly checks tire pressure, TPMS falls into the “more than I wanted or asked for” category of built-in vehicle features.  Today, tire pressures in one of my vehicles (with TPMS) were at 31 psi.  That’s down from the previous (and recommended) 35 psi, due to the outside temperature drop, but not low enough to activate the warning light.

Though I prefer using a manual gauge regularly, TPMS makes sense for typical drivers with less-stringent maintenance regimes, and even for me in the event of an unexpected pressure loss.

Readers may contact Bill Love via e-mail at precisiondriving@spokesman.com.