How Tire Pressure Sensors Work

Tire pressure monitoring systems (TPMS) are a relatively new addition to your car's suite of sensors. At least if you're old enough to remember how tire pressure monitoring was touted in the presidential election.

In fact, TPMS has been mandated by the TREAD Act since 2007 (they were earlier but not mandated), so all 2008+ model year cars are equipped with them. This is due to low tire pressure, which reduces fuel consumption and makes tires prone to damage and failure. The last two are the main security risks.

There are two types of TPMS. 

One is sensor-based and allows some drivers to have slightly more quickly available data at their fingertips. The second one is more passive, but it's still a nice bit of extra security. Here's how they work.

Two tire pressure sensor systems

The two are direct TPMS and indirect TPMS. Direct contains a sensor that transmits the actual tire pressure values ​​to the car's computer via the module. When these readings are 25% or more below the manufacturer's recommended cold pressure, the TPMS warning light on the dashboard will come on.

In some new cars, especially performance-oriented ones, drivers can often go to a screen that tells them what their tire pressure is in real-time. This is useful not only for a quick orientation but also for keeping the tires in a good place for race days and autocross.

Indirect TPMS is less involved. 

This type of system relies on the ABS wheel speed sensors already in place. If the tire is underinflated enough, it will roll at a different speed than others. This tells the car's computer that something is going on and then the TPMS warning light comes on.

In either case, the next step is to drive to a safe location and check the tires and check their pressure. They can be low for a number of reasons, but it never hurts to inflate them with a portable inflator and then see if one or more deflates again.

Advantages and disadvantages of tire pressure sensors

TPMS is a useful system that not only increases road safety but also saves some coins at the pump. Which of course means lower overall carbon emissions. However, they have their downsides.

Direct TPMS sensors send a signal and therefore need electricity to work. Batteries typically last five to ten years, and replacing them means replacing the batteries themselves or the entire sensor. Parts costs are often a bit high, plus the labor of removing and refitting the tire, which is anywhere from $15-$25 at any local tire shop, plus any additional labor to attach the new sensors with their accompanying seals and the like.

Although the advantage of indirect TPMS systems is that there are no sensors in the wheels as the variable only comes from the ABS speed sensor.

Another disadvantage of TPMS sensors is that if you choose not to install them on the second set of wheels, you will always have the TPMS warning light on. Unless you do some custom ECU coding to get rid of it, which is possible on some brand cars.

Finally, those pre-programmed for your car – such as OEM BMW sensors in BMW wheels – generally work well and require no programming. However, non-OEM options may require programming to work properly with your car.

Back to basics: 

How to extend the life of tire pressure sensors

There are two quick and easy things you can do to extend the life of your car's TPMS sensors while preventing them from triggering the warning light: keep your tires properly inflated and checked regularly, and always have the valve caps on. The former is easily done with a cheap gauge and look at the sticker in the driver's side door jamb, and the latter keeps schmutz out of the valve which slowly deteriorates it and requires replacing the valve and its sensor.