Tyre Pressure Warning Light On? What It Means
The tyre pressure warning light (TPMS) means the system has detected that one or more tyres has lower pressure than it should, or sometimes that the system itself needs resetting after a tyre change. Check all four tyres against the pressures on your door sticker as soon as it's safe, and don't ignore a light that keeps coming back.
What actually triggers the tyre pressure warning light?
Most cars built in the last fifteen years or so use a tyre pressure monitoring system that measures pressure in each tyre, either with a sensor inside the wheel or by comparing wheel speeds. When one tyre's pressure drops below the level the system expects, the light comes on. It's a measurement, not a guess — but it can only tell you that pressure has dropped, not why it dropped.
Where do I find the correct tyre pressure for my car?
Almost every car has the correct pressures printed on a sticker inside the driver's door frame, sometimes inside the fuel flap, and they're also in the handbook. It isn't the number printed on the tyre's sidewall — that's the tyre's maximum rating, not the right pressure for your car. Front and rear pressures are often different, and loaded pressures for a full car or towing can differ again.
Is it safe to keep driving with the light on?
It depends on how low the pressure has actually gone, which isn't something to judge from inside the car. A tyre a few PSI low is a nuisance to sort soon. A tyre losing air fast, or one that looks visibly low or damaged, isn't something to keep driving on — pull over and check it properly, including a look for anything stuck in the tread, before continuing the journey.
Why does the light keep coming back after I've topped up?
If the light clears and comes straight back, or keeps returning over days or weeks, that's usually a sign of a slow puncture rather than normal pressure loss from temperature changes. A nail, a flint, or a damaged valve can all cause a tyre to lose air gradually without ever looking obviously flat. Topping up repeatedly without finding the cause just delays the point where it fails properly.
Could it be the sensor rather than the tyre?
Yes — TPMS sensors are small electronic units inside the wheel, and like any electronics they can fail, especially on older cars or after a tyre change where a sensor's been knocked. A light that won't clear even when all four tyres measure correctly on a gauge usually points to a sensor or system fault rather than an actual pressure problem, and that needs diagnostic equipment to confirm, not another top-up.
Does low tyre pressure matter if the car still drives fine?
Yes — it matters even when nothing feels obviously wrong. A tyre running low wears unevenly, grips less well in the wet, and makes the engine work harder to push the car along, which shows up as worse fuel economy. None of that is dramatic enough to notice day to day, which is exactly why the warning light matters more than how the car feels from the driver's seat.
What does ONEFIX check when a TPMS light won't go out?
The tyres get checked properly against the correct pressures for that specific car, not just topped up to a round number, and if the light persists the TPMS system itself is checked with diagnostic equipment. Anything found — a slow puncture, a damaged valve, a faulty sensor — is written up in the digital vehicle health check with photographs, and a price is agreed in writing before anything is replaced.
How do I get it looked at?
ONEFIX is at Plas Acton Garage, 282 Chester Road, Wrexham, LL12 8DU, open Monday to Friday, 9:00 to 5:00. Book a tyre pressure check and, if there's a fault to fix, you'll get a written price before anything is approved.