Q: How Does My Car Monitor Tire Pressure?

All of the cars built today come equipped with a tire pressure monitoring system (TPMS). This did not become a requirement until about 2006. At that time, it was determined that a vehicle can be much safer if the driver receives notification of a low tire. If your vehicle is equipped with a TPMS, you will either get a notification of the exact tire pressure, or simply a Low Pressure Light on the dash when a tire is below a specified pressure. Although most vehicles are slightly different from one another, their TPMS systems will all work on the same principle.

The TPMS uses a special pressure sensor that is located inside of the tire. The majority if the time, this sensor is mounted on the inside of the wheel at the valve stem. On some vehicles, it is strapped to the middle of the wheel itself. No matter which kind, they work in the same way. These sensors will detect the pressure on the inside of the tire and send a signal to the computer, which allows it to calculate pressure. Some vehicles will then show the actual pressure reading on the dash, while others will only turn on a warning light when the tire pressure reaches a minimum threshold; typically around 25 psi. In such a case, the tire pressure should be adjusted in order for the light to turn off. It is important to know that on some vehicles, the light may not turn off right away; the vehicle may need to be driven at a particular speed for a certain amount of miles until the computer registers the sensor. Some spare tires will also have a pressure sensor in them, so it is important to check the air in the spare regularly.

Tire pressure sensors can fail for many reasons. A sensor may fail because the battery in it no longer functions, and needs to be replaced, but the most common cause of failure is breakage. A sensor can break from hitting something like a pothole in the road too hard, or it can be damaged when a tire is changed or repaired at a tire shop. If a sensor breaks, it will also need to be replaced. One thing that you need to keep in mind is that when a new sensor is installed, it will not automatically work with the vehicle; the vehicle’s computer needs to pick up the signal from the sensor, so the sensor needs to be programmed into the computer. This is best done with a computer scan tool by a certified mechanic.

In sum, if you get a Low Pressure Light, you need to check the air in the tires. If the tire pressure is fine, then you may have a bad sensor. It is important that you replace any bad tire pressure sensors to keep the TPMS working properly, because maintaining correct tire pressure will not only keep you safe on the road, it can also help maintain your fuel mileage.