The TPMS warning light: what it means and what to do
8 min readBy Wheel Fit
The short answer A steady TPMS light means at least one tyre is genuinely low — stop somewhere safe and check all four. A light that flashes for about a minute then stays on usually means a system or sensor fault, not a flat tyre. Those two need completely different responses.
What TPMS is
Tyre Pressure Monitoring System. It has been mandatory on new cars in the UK and EU since 2014, and it comes in two flavours that behave quite differently.
| Direct TPMS | Indirect TPMS | |
|---|---|---|
| How it works | A battery-powered sensor inside each wheel measures actual pressure | Infers pressure from wheel speed via the ABS — a deflating tyre has a smaller rolling radius, so it turns fractionally faster |
| Tells you which wheel? | Usually yes | No |
| Detects all four dropping evenly? | Yes | No — this is its main blind spot |
| Needs resetting after inflating? | Usually self-corrects | Yes, every time |
| Consumable parts | Sensors; batteries last roughly 5–10 years and are not separately replaceable | None |
Reading the light
| Behaviour | Usually means | What to do |
|---|---|---|
| Comes on steady while driving | Genuine pressure loss | Stop somewhere safe, check all four cold if possible |
| On at start-up in cold weather | Air contracting overnight | Still check and reinflate — the pressure really has dropped |
| Flashes ~60 seconds, then stays on | System fault — dead sensor battery, or a sensor missing or unpaired after a wheel change | Have the system read; pressures may be fine |
| Comes and goes | A slow puncture, or a sensor on its way out | Log pressures weekly to find which — see below |
The first cold morning of autumn
Every year the first proper cold snap sets off TPMS lights across the country. Air contracts as it cools and pressure falls with it — roughly 1 to 2 PSI for every 10°C.
That is not a false alarm. The pressure really has dropped and the tyre really is under-inflated. Top it up to the figure on the door plate rather than ignoring it, and check it again when the weather turns back.
TPMS and the MOT
What actually fails The MOT reason for rejection is a TPMS warning lamp indicating a system malfunction — not a lamp that is on because a tyre is genuinely low. If the light is on for low pressure, the system is doing its job. The check applies to M1 vehicles (passenger cars, four or more wheels, up to eight passenger seats) first used on or after 1 January 2012, and does not apply to motor caravans, ambulances or hearses over 2,500kg.
Separately, a tyre that is obviously under-inflated on a TPMS-equipped vehicle from that period is recorded as a minor defect. So the practical advice before a test is the same either way: set the pressures correctly, and get a malfunction light diagnosed rather than cleared. More on what a tester checks: tyre faults that will fail an MOT.
Never just reset it
It is tempting, especially with indirect systems where reset is a menu option. Do not. Resetting an indirect system tells the car "these pressures are correct", and it will happily calibrate itself against a genuinely flat tyre — after which it will not warn you about the thing it was fitted to warn you about.
Check and correct the pressures first, then reset.
Working out whether it is the tyre or the sensor
A light that keeps returning after you have inflated the tyre is telling you something. The way to find out what is to measure rather than guess:
- Set all four to the correct cold pressure from the door plate.
- Write down the readings and the date.
- Re-check a week later, cold, before driving.
- If one tyre has dropped, you have a leak — see why a tyre keeps losing pressure.
- If all four are holding but the light is still on, it is a system or sensor fault.
Note that a leaking TPMS sensor valve produces exactly the same symptom as a slow puncture — it is a leak, just in the sensor rather than the tread.
Sensors and tyre changes
If your car has direct TPMS, the sensors live inside the wheels. Any competent fitter works around them, but they are consumable: batteries typically last five to ten years and are not separately replaceable, and a sensor damaged during a rushed tyre change is a real cost.
Most sensors have a service kit — valve core, seal and cap — that should be renewed whenever the tyre is changed. It is inexpensive and it is the part that most often starts leaking.
Tell us when you call whether your car has TPMS so we arrive prepared. It also affects the quote — see what mobile tyre fitting costs.
Common questions
- Can I drive with the TPMS light on?
- Check the pressures first. If they are correct and the light is a system fault, the car is driveable but you have lost the warning system — get it fixed. If a tyre is genuinely low, see can you drive with a puncture?
- Do I need new sensors when I buy new wheels?
- For direct TPMS, yes — sensors live in the wheels, so a new set needs sensors fitted and paired to the car. Budget for it when pricing alloys.
- Does TPMS replace checking pressures myself?
- No. Most systems only warn at around 20–25% below the correct pressure, by which point the tyre has been running under-inflated for some time. Monthly manual checks still matter — correct tyre pressure.
- My spare has no sensor. Is that a problem?
- A space-saver normally has no sensor, and the system will usually flag a fault while it is fitted. That is expected and clears when the proper wheel goes back on.
Sources
If the light will not go away
Call 07989 606060. If it is a leak we can usually repair it at your home or workplace — see mobile tyre repair.
