As with every other aspect of the modern world, computers now monitor the air pressure in your car’s tires. While this is great for safety, and fuel economy, it has introduced new issues that owners of older cars didn’t worry about. TPMS is useful, but it is also another computer and a dozen more parts that something can go wrong with.
The TPMS system on a modern car works by having a small pressure sensor inside the wheel, typically built into the valve stem. The sensor is powered by a battery and sends out radio signals that the computer inside the car picks up. Typically there are receivers near each wheel, which tell the system when a tire is low, and which tire it is.
Keeping the TPMS Functioning
If your vehicle has TPMS, and every new car and truck in America was required to after 2007, you should take precautions to keep them functioning properly.
- Avoid aerosol flat tire repair sprays, even brands that say they are safe for use with TPMS sensors. The glue can and will gum things up and may stop them from working.
- Always use the nickel plated valve stem inserts, never raw brass ones. Brass will react with the aluminum stem, and in time become impossible to remove.
- Always use a new rubber seal between the sensor and wheel to prevent leaks.
- Avoid over-torquing the valve stem nut or you may break the stem and render the sensor unusable.
Even when cared for properly, TPMS sensor batteries don’t last forever and aren’t replaceable. They were designed to last at least 5 years, or about as long as a set of tires because changing them typically requires mounting and balancing the tires again. While the TPMS sensors were originally nearly the price of a tire itself at first, they have come down substantially. Now if you need to replace one, some aftermarket models are as low as $25.
TPMS Relearning
The simpler TPMS alerts just give you a warning light when the pressure drops 25% below the set level. On these cars, typically lower cost models, you have to manually check all 4 tires to see which one is low. That may seem like a hassle, but it makes other maintenance tasks easier, like tire rotations.
On the more advanced systems, the computer will tell you exactly what the tire pressure is in each wheel and warn which tire it is when one goes down. The negative of these systems is that when you rotate the tires the system needs to relearn which one is where. These systems also need to relearn when sensors are replaced, or new wheels are fitted.
These days most tires shops know the ins and outs of linking the TPMS with the sensors, and typically will do it with a tire rotation or replacement. Of course, your dealer will be happy to do it as well, but it will cost more.
Some cars, most notably GM and Ford products, don’t require anything more than a little knowledge and the key fob (for GM vehicles) to reset the system. On many Fords, turn the ignition to "on" (or press the start button without stepping on the brake), then press the hazard light button quickly 6 times. On most GM cars and trucks, turn the key to the "on" position, and press the lock and unlock buttons on the fob at the same time.
From there both are similar. The Ford will indicate on the dashboard, and the GM will light a turn signal bulb, to show which corner to start with. Let air out of the tire in that position until the horn toots, then move to the next indicated tire. When all 4 are done, the horn will beep twice. Of course, now you have to reinflate the tires to the recommended level.
