Last week I explained why our vehicles are equipped with a tire pressure monitor system (TPMS). This week, let’s look at how these systems work.
There are two different types of TPMS systems used in today’s vehicles.
The simpler system uses information from the wheel speed sensors of the anti-lock brake system (ABS) system to identify a low tire. A tire that is low on pressure will be slightly smaller and will need to rotate at a faster speed to keep up with the properly inflated tires. The ABS control module will pick up this difference in rotational speed and trigger the low tire warning light to illuminate.
This type of system will not tell the driver which tire is low or the pressure of the tire, only that pressure is low in one or more tires. When the warning light illuminates, the tires should be checked for the proper pressure as soon as it is safe to do so. When the tires are rotated or replaced, there is no tire location relearn procedure for this type of TPMS system.
The second type is a more sophisticated system that uses a pressure sensor in each tire. These sensors are commonly a part of the valve stem and transmit a wireless signal to an on-board receiver. These systems will commonly display the tire pressure for each tire on the dash or driver information center (DIC) display. If the tire pressure falls outside of a preset range, a check tire pressure message will be displayed and/or a warning light will illuminate.
When the message or warning light displays, the tire pressure can be checked on the dash display. With this type of system, the receiver must “learn” the location of each of the tire pressure sensors. When the tires are rotated or replaced, the relearn should be performed so the tire pressure display will be correct.
When the low tire warning message or light is displayed, it should not be ignored. Tire pressures should be inspected as soon as it is safe to do so. Until the pressure can be checked, the driver should be extra aware of any changes in the vehicles handling and pull over when something doesn’t feel right.
A faulty wheel speed or tire pressure sensor can cause a false low tire warning message. If this happens, the system should be diagnosed and repaired as necessary so the driver will be properly warned when there is indeed a low tire.