Key takeaways
- TPMS stands for Tyre Pressure Monitoring System — it warns you when a tyre is significantly under-inflated.
- The most common cause of the light is genuinely low pressure, so check and reset all four tyres first.
- A steady light usually means low pressure; a flashing light often means a TPMS sensor fault.
- On cars first used from 2012, a faulty TPMS is an MOT failure, so a broken sensor must be fixed.
The tyre pressure warning light catches a lot of drivers out — it looks like a horseshoe with an exclamation mark, and it can mean anything from a genuinely flat tyre to a sensor that needs replacing. Ignoring it is risky, because under-inflated tyres are dangerous and a TPMS fault will fail your MOT. Here is what the light means and how to deal with it.
Why is my tyre pressure warning light on?
The most common reason the tyre pressure light comes on is that one or more tyres really is under-inflated, so the first step is always to check and correct all four pressures. If they are correct and the light stays on, the cause is usually a TPMS sensor or system fault rather than the tyres themselves. Cold weather can also trigger it.
TPMS — the Tyre Pressure Monitoring System — exists to warn you before low pressure becomes dangerous. So treat the light as a prompt to check the tyres straight away, not something to clear and forget.
What is TPMS and how does it work?
TPMS is a system that monitors your tyre pressures and alerts you when one drops too low. There are two types. Direct TPMS uses a pressure sensor inside each wheel that radios readings to the car. Indirect TPMS has no sensors; it estimates pressure from how fast each wheel turns, using the ABS, since a soft tyre rolls at a slightly different rate.
Direct systems are more precise and can often tell you which tyre is low, but their sensors have batteries that eventually run flat, usually after several years. Indirect systems have nothing to wear out but must be reset manually after you adjust pressures or rotate the tyres. TPMS has been fitted to new cars in the UK for over a decade.
Steady light or flashing light?
How the light behaves tells you a lot. A steady, constant warning light usually means at least one tyre is genuinely low on pressure and needs attention. A light that flashes for a while when you start the car and then stays on usually signals a fault in the TPMS itself — most often a failed sensor or a flat sensor battery.
| Light behaviour | Likely meaning | What to do |
|---|---|---|
| Steady / constant | A tyre is under-inflated | Check and reset all four pressures |
| Flashing then steady | TPMS sensor or system fault | Have the sensors diagnosed |
| Comes on in cold weather | Pressure dropped with temperature | Top up to the correct cold pressure |
| On after a tyre change | Sensor not reset or damaged | Reset the system or check the sensor |
How do you turn the tyre pressure light off?
If the light is on, set every tyre to the correct cold pressure first, using your handbook or the door-pillar sticker — see our guide on how to check and set tyre pressure. On many cars the light then goes out after a short drive; on others you trigger a reset from the dashboard menu. If it still will not clear, a sensor likely needs attention.
- Set all four tyres (and any monitored spare) to the correct cold pressure.
- Drive for a few minutes — many systems reset themselves automatically.
- If needed, run the reset procedure from your car's menu or handbook.
- If the light returns or flashes, suspect a faulty or flat-battery sensor.
Why a TPMS fault matters for your MOT
A working TPMS is a legal requirement on cars first used from 1 January 2012, and a faulty system is an MOT failure. The DVSA testing rules mean a TPMS warning light staying on, or a system that is obviously not working, will fail the test. So a dead sensor is not something you can simply ignore — it must be repaired to keep the car road-legal.
Getting a TPMS fault fixed
If the light is down to a faulty or flat-battery sensor, the sensor needs replacing or servicing — often done at the same time as fitting a new tyre or valve, since the sensor lives inside the wheel. Our mobile TPMS replacement service can diagnose and replace sensors at your location, and we handle valve replacement too. If the light is simply low pressure, a quick top-up is all it takes — checking first costs nothing.
Frequently asked questions
It is usually an amber symbol shaped like a horseshoe or a flat cross-section of a tyre, with an exclamation mark in the middle. Some cars instead show a top-down car outline with a low tyre highlighted, or a written warning message on the dashboard.
Treat it as a warning to check your tyres promptly. A steady light usually means low pressure, which is unsafe and wastes fuel, so check and correct it as soon as you safely can. A sudden light could mean a puncture, so reduce speed and inspect the tyres.
Tyres can be significantly under-inflated while still looking normal, so always check with a gauge rather than by eye. Cold weather can also lower pressure enough to trigger the light. If pressures are correct and it stays on, suspect a TPMS sensor fault.
Direct TPMS sensors have a built-in battery that typically lasts several years before it runs flat, after which the sensor needs replacing. They can also be damaged during tyre fitting. Indirect systems have no sensors to fail but must be reset after adjusting pressures or rotating tyres.
Yes. On cars first used from 1 January 2012, the TPMS is checked at MOT, and a warning light that stays on or a system that is clearly not working will fail. A faulty sensor must be repaired to keep the car road-legal, not just reset or ignored.
Yes. Because the sensor sits inside the wheel, it is usually replaced when the tyre is off, which our mobile team can do at your home, work or the roadside. We can diagnose the fault, fit a new sensor and reset the system on site.