What is this mysterious light? It’s the TPMS warning!


September 29, 2012 by quirkyuncle

TPMS monitoring light

The Tire Pressure Monitoring System (TPMS) in your car lets you know if there is a potential problem with the inflation level in your tires. If you see this light, you need to check your tire pressure as soon as it is safe to do so. If your car also feels funny or is making odd noises when the light comes on, you should pull over ASAP and see if one of your tires is really low.

The TPMS was first installed in production cars in 1986. It is mandatory for all passenger cars starting with the 2008 model year. The newer your car is, before 2008, the more likely it will have a TPMS.

Most TPMS have a pressure sensor inside each tire that sends tire pressure information, via radio, to the car’s computer. Some cars do not have these sensors, but instead monitor differences between how much each of the four wheels rotate in relation to each other, using the car’s anti-lock brake system (ABS) sensors – a wheel that consistently rotates more than the others would have a lower tire pressure.

The tire pressures in your car can trigger the TPMS light for the following reasons:

  • Temperature changes – seasonal temperature changes can trigger the TPMS. In this case, there isn’t anything wrong at all. Adjust your tire pressure, reset the TPMS system, and you’ll be fine.
  • Leaky tire – Tire leaks can range from catastrophic to minimal. If the leak is bad enough, the tire won’t be able to hold air and will need to be changed before you can drive the car. (The only exception is run-flat tires, installed on some cars, which can be driven for limited distance with no air at all.) If the leak is smaller, you might be able to inflate the tire and drive the car for a bit, until you can get the tire fixed. Some tires just leak very slowly for no apparent reason and just need to be checked on a more regular basis. I’ll be discussing how to diagnose and change a flat or leaking tire in another posting. Check back soon!
  • Bad sensor or sensing system – If all the tire pressures are good, the light comes on again after resetting the system, and the tire pressures check OK again the second time, there might be a problem with one of your sensors or other TPMS system components. Check with your mechanic or tire dealer about how to correct this issue.

TPMS cautions
Extra care needs to be taken on cars with a TPMS:

  • Special procedures need to be followed by your tire dealer, so they don’t damage the sensors when mounting the tires on the wheel.
  • Avoid using the canned tire repair systems that inject rubberized sealant into the tire, as these can ruin the in-wheel sensors. Some sealants are advertised as TPMS safe. Try to use these, if you absolutely need to follow this roadside repair approach.
  • Having a TPMS in your car does not eliminate the need for performing normal tire maintenance. You still need to check and adjust your tire pressure on a regular basis.
  • The TPMS system should always be reset after adjusting your tire pressures. There is a button on your instrument panel that does this. See your owners manual for instructions.
    Reset TPMS


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