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. Direct systems can show a live pressure for each wheel; indirect systems can only tell you that something has changed.
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. If your car has TPMS, mention it when you book so the fitter knows before the tyre comes off.
How to reset the TPMS light
Set all four tyres to the placard pressure first, then reset. Resetting before you correct the pressures teaches the system that a low tyre is normal. The exact method depends on which type of system the car has.
- Correct the pressures cold, including the spare if it has a sensor (some do).
- Indirect systems: find the reset in the driver menu or a button near the steering column, often labelled TPMS, SET or with the tyre symbol. Hold or confirm it, then drive for 10 to 20 minutes at normal road speeds so the system can learn the new wheel-speed baseline.
- Direct systems: most clear themselves after a few minutes of driving once every tyre reads correctly. Some cars need a relearn from the menu, and a few need a fitter's tool to pair a new sensor.
- Still on after a 20-minute drive? One tyre is still low, one is losing air, or a sensor has failed or lost its pairing.
The handbook lists the method for your model; it is usually a two-minute job. If a warning comes back within days after a reset, treat it as a slow puncture until proved otherwise.
Reset guides by model
The menu path and the relearn drive differ from car to car. These step-by-step guides cover popular models:
- Audi A3
- BMW 1 Series
- BMW 3 Series
- Fiat 500
- Ford Fiesta
- Ford Focus
- Ford Kuga
- Hyundai Tucson
- Kia Sportage
- Mercedes A-Class
- Mini
- Nissan Qashqai
- Peugeot 208
- Renault Clio
- Toyota Yaris
- Vauxhall Astra
- Vauxhall Corsa
- Volkswagen Golf
- VW Polo
Direct vs indirect: which does your car have?
If your car shows a pressure figure for each tyre on the dashboard, it has direct TPMS. If it only shows a warning light, it is probably indirect. The difference matters when something goes wrong, because the two systems fail in different ways and cost different amounts to put right.
| Direct TPMS | Indirect TPMS | |
|---|---|---|
| How it works | Battery-powered sensor in each wheel measures real pressure | ABS wheel-speed sensors spot a tyre turning faster because it is smaller when soft |
| What it can show | Each tyre's pressure, often which tyre is low | A warning only, usually without saying which tyre |
| Weak spot | Sensor batteries die after several years; sensors can be damaged during tyre changes; corrosion at the valve | Slow to react, misses all four tyres going down evenly, needs resetting after every pressure change |
| Extra cost at a tyre change | Service kit for each sensor; occasional sensor replacement | None |
| Seasonal wheel swap | Second set of sensors needed in the winter wheels | Nothing extra |
Both types have been mandatory on new cars sold in the UK and EU since November 2014, which is why cars from the mid-2010s onwards nearly all have one or the other. What a failed sensor involves is covered in TPMS sensor replacement cost.
What the light cannot tell you
TPMS warns about pressure and nothing else. It will not tell you about a bulge, a cut, low tread or an ageing tyre, and most systems only trigger once a tyre is well below its set pressure. Treat it as a backstop, not as a substitute for looking at your tyres.
- It comes on late. Most systems warn at roughly 20 to 25 per cent below the set pressure, by which point grip, wear and fuel economy have already suffered. A monthly gauge check catches problems the light will not.
- It cannot see damage. A sidewall bulge or a nail that has not yet started leaking gives no warning at all. The 20p test and a quick walk-round still matter.
- A sudden light while driving is different. If the warning appears and the car starts to pull or feel odd, that is a fast leak. Slow down, stop somewhere safe and look before going further. See our flat tyre help page.
- A light that comes on after a cold night and goes off by lunchtime is usually just physics, but it still means the tyres are on the low side of correct. Top them up.
The legal position does not change because a light is or is not on: a tyre must be properly inflated and in good condition, as set out on GOV.UK.
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.
