What is a TPMS Sensor & How Does It Work?
It’s never good to drive around with under-inflated tires, it’s bad for fuel economy and it’s bad for safety. That’s why car manufacturers have developed Tire Pressure Monitoring Systems (TPMS). First introduced in 1986, but only for high-end luxury and performance vehicles, the TPMS spread to the rest of the automotive market when it became a legal requirement in 2007. There are two different versions of these systems, Indirect and Direct, so we’ll take a closer look to see what sets them apart from one another.
Indirect TPMS
An Indirect TPMS system works in conjunction with the ABS system, sharing the data from the wheel speed sensors. While a sudden and extreme change in wheel speed tells the ABS system that a wheel is either slipping or has locked, a persistent difference in wheel speeds is an indicator of an underinflated tire. This kind of piggybacking keeps the cost of the system low, both in terms of initial cost and maintenance, The downside is that it isn’t actually measuring tire pressure, so things like uneven tire wear or installing a tire in a different size can throw it off. The system also needs to be reset after every tire rotation, or even just after inflating your tires.
Direct TPMS
A much more accurate way of monitoring tire pressure is a Direct TPMS. This system relies on dedicated sensors that sit inside the tire and monitor actual tire pressure. Uneven wear patterns and different-sized wheels won’t cause issues with a Direct TPMS system, and the sensors don’t need to be reset so frequently. The sensors themselves work wirelessly and therefore require a battery. Battery life is good, typically lasting about a decade, although when a battery wears down, it usually requires the whole sensor to be replaced. This is part of what makes Direct systems more expensive than Indirect systems.
TPMS Warning Lights
There are a few different types of tire pressure warning lights, but the most common is a horseshoe-shaped icon with an exclamation mark in the middle. There could also be a light that just says “TPMS”, and sometimes it will be a combination of the two. This could mean either that a tire is low, or that there is a problem with the sensor itself. This can be verified by manually checking the pressure of each tire, and this is something that should be done regularly anyway, since sensors aren’t always 100% accurate. Whatever the issue, if you have a TPMS dash light on, we strongly recommend that you contact our service department, as this could potentially be a serious safety issue.