Tyre pressure monitoring – TPMS
TPMS (Tire Pressure Monitoring System) is a system fitted in all cars from November 2014 onward. It's designed to give the driver information about the tyre pressure while driving. There are two basic types of TPMS on the market:
- Indirect TPMS measures differences in rotation speed between the wheels via the ABS system. It shows a symbol when the pressure has dropped in a tyre.
- Direct TPMS measures the air pressure in all tyres (sometimes the spare too) via sensors in each wheel. With this system the car indicates exactly which tyre has lost pressure, and usually also shows the current pressure in the tyres. Sensors for direct TPMS systems can be either programmable or self-programming. The sensors have a battery with a lifespan of around 5 years; once it runs out, the whole sensor needs replacing.
Resetting the TPMS system
It's common for the tyre-pressure warning light to come on after fitting new tyres or switching to summer/winter tyres, which means the system needs to be reset so it can read the new tyres. Some cars do this by themselves, while others need a manual reset.
On most cars that require a manual reset, you can do it yourself easily through one of the car's menus. Check your owner's manual for how to do it on your car. On some cars, a workshop needs to help reset the system with a special diagnostic tool.
TPMS light stays on even though the pressure is correct?
There are a few different things that could have happened, depending on whether you have an indirect or a direct system.
With an indirect system, this most commonly happens alongside the ABS light coming on, since tyre-pressure monitoring is done via the ABS sensors. If the ABS light isn't on at the same time, it's usually a problem with the car's computer, and you should visit an authorised workshop.
With a direct system, the most common fault is that one of the sensors isn't working because its battery has run out. Sensors have a lifespan of around 5 years, but it varies. To check the sensors, you can visit a tyre workshop with a TPMS reader that can check them all and see if one isn't working. Otherwise it could be a problem with the car's computer, and you should visit an authorised workshop.
What is the purpose of the TPMS system?
The system improves road safety by warning when a tyre is losing air before it goes completely flat and becomes a road hazard. It also reduces fuel consumption, since you can always make sure the pressure is correct. Tyre pressure has a big effect on the car's handling and the tyres' lifespan.