TPMS Light On: Will It Fail Your MOT?

Two lamps that look identical

The horseshoe-shaped symbol with an exclamation mark inside it is doing two different jobs, and the difference decides whether you fail.

• Steady from the moment you set off: the system is reporting low pressure. It thinks a tyre is soft. Usually it is right.
• Flashes for around 60–90 seconds at start-up, then goes steady: that flash-then-steady sequence is the standard way a car reports that the monitoring system itself has failed — a dead sensor, a sensor that is not paired to the car, or a receiver fault. This is the version that fails an MOT.

The distinction is worth knowing before you book anything, because the two have entirely different fixes and entirely different costs. One is free at a garage forecourt airline. The other is a workshop job.

How often it actually fails cars

Less often than the other assessed lamps, but it is far from rare, and the pattern is revealing: 1,762 vehicles carried the TPMS entry as an advisory against 737 as a failure. Advisories on this item outnumber failures by a wide margin, which is what you would expect from a system where testers frequently see a lamp caused by pressure rather than by a fault.

Looked at by model rather than by vehicle, a faulty TPMS ranks among the five most common MOT failure items on 107 UK make/model records covering 1,913,383 tests, where it accounts for a sample-weighted 1.31% of tests — and as much as 6.3% on the worst-affected model. Cars that reach the age where the original sensor batteries die tend to reach it all at once.

What to do before the test

Start with the free half. Set all four tyres — and the spare, if it has a sensor — to the pressures on the plate in the driver's door shut or inside the fuel flap, measured cold, before you have driven more than a couple of miles. Warm tyres read high, so setting them at the end of a motorway run leaves them under-inflated when they cool.

Then drive it. Most systems need several minutes of movement above roughly 15–20mph to re-read all four wheels, so a lamp that is still on in the car park does not yet mean anything is broken. If the car has a reset function, run it after you have set the pressures, not before.

If the lamp survives that, it is a system fault, and on a 2012-or-later car it is a failure item. Have the sensors read — any tyre shop can do it in minutes with a TPMS tool that shows which corner is not responding. Check whether the car has previously been flagged: a free MOT history check will show whether a TPMS advisory has already appeared at an earlier test, which is usually the year before it becomes a failure.

Do not treat it as a warning you can wait out

TPMS exists because drivers are bad at noticing under-inflation. A modern low-profile tyre can be 20% down on pressure and look completely normal, and that is enough to lengthen your stopping distance, ruin the tyre's shoulders and build heat in the sidewall. If the lamp is on and a tyre is genuinely soft, find out why it is soft — a tyre that needs air every week has a puncture, and a slow puncture is a fast one that has not happened yet.

What the MOT record shows

Frequently asked questions

Before you spend anything on diagnostics, check what this car has already been failed for. A free MOT history check returns every failure and advisory on the registration in the tester's own words — including whether this lamp has been recorded before.