TPMS Explained: What Your Tyre Pressure Warning Light Means
The TPMS (tyre pressure monitoring system) warning light tells you that one or more tyres has lost pressure. It became standard on new cars from 2014. When it comes on, check and correct all four pressures as soon as it is safe; common causes are a cold-weather pressure drop or a slow puncture.
What TPMS is and why cars have it
TPMS stands for tyre pressure monitoring system. It warns you when a tyre is significantly under-inflated, helping prevent the poor grip, extra fuel use, faster wear and blowout risk that under-inflation causes.
It has been mandatory on new cars sold in the UK and EU since 2014. The aim is simple: most drivers do not check pressures often enough, so the car keeps an eye out and flags a problem before it becomes dangerous.
Direct vs indirect systems
There are two types. Direct TPMS uses a sensor inside each wheel that measures actual pressure and reports it, sometimes showing a figure for each tyre on the dashboard.
Indirect TPMS has no sensors; instead it uses the ABS wheel-speed sensors to spot a tyre that is rotating slightly faster because it is under-inflated and smaller. Indirect systems usually need resetting after you adjust pressures or change a tyre, which is done through the car's menu.
Why the light comes on
The most common reasons the TPMS light appears are straightforward.
- A cold-weather pressure drop, common on the first frosty mornings.
- A slow puncture from a nail or screw.
- A natural gradual loss of pressure over weeks if you have not checked.
- A faulty valve or sensor, especially on older cars.
Start by checking and correcting all four pressures.
What to do when it appears
When the light comes on, reduce speed and avoid hard braking or cornering until you can check the tyres, as one may be significantly low. As soon as it is safe, check all four pressures cold and inflate to the figure on your door-sill label or handbook.
If a direct system shows individual pressures, you can see which tyre is low. After correcting pressures on an indirect system, you may need to reset it through the menu so it relearns the correct baseline.
When the light will not go off
If the light stays on or keeps returning after you have set all pressures correctly, something else is going on. A slow puncture will let a tyre drop again within hours or days, so have it checked for a nail or valve leak.
On direct systems, the in-wheel sensors contain batteries that last several years; a failed sensor keeps the light on regardless of pressure and needs replacing. We can diagnose whether it is a leak, a valve or a sensor fault.
TPMS and your MOT
A TPMS that is not working, or a warning light that stays on, is an MOT failure on cars first used from 2012 onwards. So it is not something to ignore or cover over; it needs putting right.
If your light is on and you are not sure why, pop in and we will check your pressures, look for a puncture, and test the sensors. Often it is a simple top-up or a quick repair, and we will get the system working and the light off properly.
Frequently Asked Questions
What does the tyre pressure warning light mean?
It means the TPMS has detected that one or more tyres is significantly under-inflated. Check and correct all four pressures cold as soon as it is safe. Common causes are a cold-weather pressure drop or a slow puncture, so if the light returns after topping up, have the tyre checked.
Why won't my TPMS light go off after pumping up the tyres?
If the light stays on after correcting pressures, you may have a slow puncture letting a tyre drop again, an indirect system that needs resetting through the menu, or a failed sensor whose battery has run out after several years. Have it checked to find which it is.
Is a TPMS warning light an MOT failure?
Yes. On cars first used from 2012, a TPMS that is not working or a warning light that stays illuminated is an MOT failure. It also signals a real tyre issue, so it should be diagnosed and put right rather than ignored or taped over.
Do I need to reset TPMS after changing pressures?
On indirect systems, which use the ABS sensors, you usually need to reset the system through the car's menu after adjusting pressures or changing a tyre so it relearns the baseline. Direct systems with in-wheel sensors generally update on their own once pressures are correct.
How long do TPMS sensors last?
The sensors in direct systems contain a battery that typically lasts several years, often around five to ten. When one fails, the warning light stays on regardless of actual pressure, and the sensor needs replacing. We can test the sensors and confirm whether one has reached the end of its life.
Book With Norwich Tyres & Auto Service
Need a hand from a real, independent Norwich garage? Call 07933 900901 or pop into Ber Street, NR1 3ES. Same-day tyre fitting is available on most common sizes, with free parking on site.
Hero image: “Low fuel warning light.” by MIKI Yoshihito. (#mikiyoshihito) (source), licensed under CC BY.