Tyre Pressure Warning Light: What It Means and What To Check First
The TPMS light means at least one tyre is reading low, or the monitoring system itself has a fault. Most of the time the fix is free air at a petrol station, and if a sensor has died it is £40-90 plus fitting. On cars first used from 2012 the light is an MOT failure, so it cannot just be lived with.
What it means
Tyre pressure monitoring comes in two types. Direct systems have a battery-powered sensor inside each wheel measuring actual pressure. Indirect systems use the ABS wheel speed sensors to spot a tyre rolling on a smaller circumference than the others, which is what a soft tyre does. Both put the same light on.
A steady light normally means low pressure in one or more tyres. On direct systems, a light that flashes first and then stays on usually means a sensor fault rather than a soft tyre, often a sensor whose internal battery has died, they last roughly five to ten years.
Can you keep driving?
Amber, but check the tyres before any real journey. The light cannot tell you the difference between a tyre a few PSI down and one going flat fast with a screw in it. Stop somewhere safe, walk round the car, and look for an obviously soft tyre. If all four look normal, drive gently to a petrol station, set all tyres to the pressures on the sticker in the door shut, and reset the system if your car requires it. If a tyre is visibly deflating or you can hear air, deal with it there and then, driving on a flat destroys the tyre and can damage the wheel.
Most common causes
- Natural pressure loss, tyres lose air slowly and drop further in cold weather
- A puncture, often a slow one from a screw or nail
- Dead TPMS sensor battery on direct systems
- Sensor damaged during a tyre change
- System not reset after adjusting pressures or changing wheels
- Corroded sensor valve stems, a known issue on older alloys
What it costs to fix
| Repair | Typical UK independent garage price |
|---|---|
| Air top-up | Free or a few pence |
| Puncture repair | £20-35 |
| TPMS diagnostic/reset | £50-95 |
| TPMS sensor | £40-90 each plus fitting |
| New tyre (if unrepairable) | £60-180 depending on size |
Will it fail the MOT?
Yes, on newer cars. For cars first used on or after 1 January 2012, an illuminated TPMS light indicating a malfunction is a major defect and an MOT failure. On older cars the light is not testable, though a dangerously deflated or damaged tyre fails on its own merits at any age. So on a 2012-on car, a dead £40-90 sensor has to be replaced, not ignored.
Common questions
I put air in but the light is still on. Why?
Two usual reasons. Many cars need the system reset or recalibrated after pressures change, check the handbook for a TPMS set button or menu option. If it still returns, either one tyre has a slow puncture and is dropping again, or a sensor has failed, and a garage or tyre shop can read which wheel is reporting in minutes.
Why does the light come on more in winter?
Air contracts as it cools, and tyre pressure drops by roughly one to two PSI for every ten degrees the temperature falls. A tyre that was borderline in October reads low on the first cold morning. It is real low pressure, not a false alarm, so top up rather than ignore it.
Do I have to replace TPMS sensors when I buy new tyres?
No, the sensors live on the wheel, not the tyre, and normally carry straight over. It is worth replacing a sensor at tyre-change time if its battery is near the end of its life, since the labour overlaps, but a tyre shop insisting all four must be renewed as routine deserves a second opinion.