On vehicles equipped with indirect TPMS, instead of utilizing sensors in each wheel, tire pressure is calculated by comparing relative wheel speeds, using the signals from ABS sensors.

Before diving right in to look at ABS signals, check to make sure that all of the tires on the vehicle are the same size, and that one is not excessively worn over the rest. In addition, don’t be fooled to think that a car with rubber valve stems automatically has an indirect TPMS system. From time to time, bad TPMS components get pitched and replaced with the aforementioned by penny-pinching car owners who are happy to live with the warning light. This can also be common with aftermarket wheels, and if your customer has bought a car like this, they may not realize the problem.

If you happen to see this, don’t forget, it’s illegal to disable TPMS in any way, and it’s a gray area if you don’t fix it, so be sure your customer is well aware of the problem and signs off on a refused repair.