Tire Pressure Monitoring System: TPMS Light & Law 2026

A steady tyre pressure light means at least one tyre is too soft. A light that flashes and then stays on means the monitoring system itself has a fault. In both cases, check all four tyres with a gauge before you drive on. In the UK a system fault can fail the MOT, but a light caused only by low pressure is not a fault.

TPMS warning light: what each Tyre (Tire) signal means

The tyre pressure monitoring system (TPMS) symbol is a tyre cross-section with a flat bottom and an exclamation mark, usually in amber. Most cars use the same lamp for two jobs. It shows low pressure with a steady light, and a system fault with a flashing light that then stays on. Your handbook confirms which pattern your car uses. Some cars also show a text message or a pressure reading for each wheel.

The light is a warning, not a pressure gauge. It only comes on once a tyre is already well below its set pressure, so it will not catch a tyre that is a little low. It also cannot tell you whether a tyre is overinflated, worn or damaged. Check your pressures by hand on a regular schedule even if the light never comes on. The tyre pressure guide explains how.

Direct and indirect tire pressure sensors

Direct TPMS has a battery-powered sensor inside each wheel, usually fixed to the back of the valve. Each sensor sends pressure (and on many cars temperature) to the car by radio. These are the parts people mean when they search for “tire pressure sensors”. The battery is sealed inside the sensor, so when it runs flat the whole sensor is replaced.

Indirect TPMS has no sensor in the wheel. It uses the ABS wheel-speed sensors to notice when one tyre turns faster than the others, which happens when that tyre has lost pressure and its rolling diameter has shrunk. It costs nothing to maintain, but you must reset it every time you change the pressures or the tyres. It can also miss all four tyres losing pressure slowly at the same rate.

Pressures may be shown in bar, psi or kPa depending on the car’s market and settings. The tyre pressure calculator converts between these units and gives you a target pressure for your load.

Resetting tire pressure sensors

• Indirect systems: inflate all tyres cold to the pressure on the door-pillar or fuel-flap placard. Then use the reset button or the vehicle-settings menu and drive normally while the system learns the new baseline.
• Direct systems: the light normally clears by itself after a short drive once the pressures are correct. You do not press any reset button.
• After new sensors, a wheel swap or a seasonal wheel change: many direct systems must learn the new sensor IDs or positions. Depending on the car this happens automatically while driving, through a procedure in the handbook, or with a diagnostic tool at a tyre shop.

If the light comes back on soon after a correct reset, the tyre is probably still losing air. Find out why rather than resetting the system again.

What tyre pressure sensors cost depends on

There is no single price. Replacing a direct sensor usually includes the sensor itself, removing and refitting the tyre, balancing, and programming or pairing the sensor to the car. Many manufacturers also recommend fitting a new valve core, seal and cap whenever the tyre comes off. For the same reasons, a second set of wheels for winter costs more on a car with direct TPMS. Indirect systems have no sensor parts to buy.

TPMS law in the US, UK, Canada and Australia

United States. A federal motor vehicle safety standard requires TPMS on new light vehicles. It must include a low-pressure warning and a malfunction indicator. Whether a lit TPMS lamp matters at a periodic inspection depends on the state, so check with your state’s inspection programme.

United Kingdom. The MOT checks that a fitted TPMS is not obviously inoperative and that the lamp does not show a system malfunction. Either one is a reason for rejection. The check only applies to passenger vehicles within the scope set out in the MOT inspection manual, so older cars are not tested for it. A lamp that is on only because a tyre is low is not counted as a malfunction. Inflate the tyre and let the lamp clear before the test. Taking out the sensors (for example when fitting aftermarket wheels without them) leaves an in-scope car with an inoperative system.

Canada. New-vehicle safety standards are set federally by Transport Canada, and inspection rules are set by each province. Ask the inspection station whether a TPMS fault is checked.

Australia. Roadworthy and safety inspections are run by each state and territory. Rules for warning lamps on the dashboard vary, so ask the inspection station before you book.

Drive, check or repair?

Some sensor makers warn that aerosol puncture sealants can clog or damage direct sensors. Tell the tyre shop if you have used one.

Sources

• DVSA, Matters of Testing blog: MOT tester guidance on warning lamps and TPMS reasons for rejection (mattersoftesting.blog.gov.uk)
• DVSA MOT inspection manual, tyre pressure monitoring system section (gov.uk)
• Vehicle owner’s handbooks for lamp patterns and reset procedures