The TPMS warning light, a horseshoe shape with an exclamation mark, tells you a tyre is significantly under-inflated, or that the monitoring system itself has a fault. It's not a light to ignore: on cars first used from 1 January 2012, a malfunctioning TPMS is an MOT failure, so it affects both your safety and your test.
Here's what the system actually does, how to read a steady light versus a flashing one, the right steps to take, and how it ties into your MOT.
What TPMS does
Tyre Pressure Monitoring Systems alert you when a tyre loses pressure, before it becomes obvious or dangerous. There are two types: direct systems use a sensor inside each wheel to read actual pressure, while indirect systems infer low pressure from wheel-speed data via the ABS. Knowing which you have helps explain how the light behaves and what's involved if it needs fixing.
Steady light vs flashing light
The way the light behaves tells you roughly what's wrong:
- Steady light: usually a genuinely low tyre. Check and correct all four pressures.
- Flashing then steady: often a system fault, such as a failed sensor or one that needs reprogramming after a tyre change.
A steady light is the more common and more straightforward of the two, and it usually clears once the pressures are corrected. A flashing light that settles to steady is the one that points to the system rather than the tyre.
What to do
Work through these in order before assuming the worst:
- Check all four pressures when cold and set them correctly.
- Look for a slow puncture if one tyre keeps dropping.
- Remember cold weather can trip the light, so top up and it may clear on its own.
- If the light stays on after correct inflation, a sensor likely needs service.
Sensors and tyre changes
Direct TPMS sensors have batteries that eventually die, usually after several years, and they sometimes need reprogramming or "relearning" after a new tyre is fitted. A sensor can also be damaged during a careless tyre change, which is one more reason to have tyres fitted by someone who handles TPMS properly. We check and reset TPMS sensors when we fit tyres at your location across the UK, so you don't leave with a warning light on.
TPMS and the MOT
For cars first used from 1 January 2012, a TPMS that isn't working correctly is an automatic MOT failure (GOV.UK). That means an ignored warning light won't just cost you safety, it'll cost you the test. If your light is on, get it sorted before the MOT rather than discovering it on the day. It's a quick fix in most cases, either correcting the pressures or servicing a sensor.
