TPMS Sensors Explained: The Tyre Pressure Warning Light

Published 2026-04-23 · Park Royal Tyre & Alignment Centre

That little horseshoe-shaped symbol with an exclamation mark inside it catches plenty of drivers off guard. It's the tyre pressure warning light, and it's powered by a system called TPMS. Since 1 November 2014, all new passenger cars sold in the UK and EU have been required to have a Tyre Pressure Monitoring System fitted, under EU Regulation 661/2009. Knowing how it works, why it triggers, and what it means for staying road-legal can save you money and keep you safer on the road. Here's a clear, jargon-free guide from our workshop in Park Royal.

What is a TPMS and what does it do?

A Tyre Pressure Monitoring System constantly checks the air pressure in your tyres and warns you when it drops too low. It became mandatory on new UK and EU cars from 1 November 2014 under EU Regulation 661/2009. Underinflated tyres are dangerous: the National Highway Traffic Safety Administration found they are three times more likely to be involved in a tyre-related crash.

The system exists because we're not very good at spotting low pressure by eye. A tyre can lose a noticeable amount of air before it looks flat. TPMS removes the guesswork by alerting you on the dashboard, so small problems get fixed before they become blowouts or expensive tread damage.

Why does the tyre pressure warning light come on?

The light comes on when at least one tyre falls roughly 25% below its recommended pressure, the threshold many systems use to trigger an alert. Cold weather is a common, harmless cause: tyre pressure drops by around 1 to 2 PSI for every 10°C fall in temperature. A slow puncture, a faulty valve, or a dead sensor battery can also be behind it.

There's a useful difference to watch for. A steady light usually points to genuine low pressure. A light that flashes for around 60 to 90 seconds and then stays on often signals a system fault, such as a failed sensor. In our experience, drivers frequently top up the air and feel puzzled when the light stays lit, which is often a sensor issue rather than a pressure one.

Direct vs indirect TPMS: what's the difference?

There are two designs, and they behave quite differently. Direct TPMS uses a battery-powered sensor inside each wheel that measures actual pressure and radios it to the car. Indirect TPMS has no sensors at all; it uses the ABS wheel-speed sensors to detect when an underinflated tyre rotates at a slightly different rate to the others.

Direct systems

Direct sensors give accurate, per-wheel readings, and many cars display the exact pressure for each tyre. The trade-off is cost: the sensors contain a sealed battery that typically lasts five to ten years, after which the whole sensor needs replacing.

Indirect systems

Indirect systems are cheaper because they reuse existing ABS hardware. The catch is that they must be reset manually after you inflate or change a tyre, and they can be slower to spot a gradual, even loss of pressure across all four wheels.

Does TPMS need servicing when you change tyres?

Yes, and it's the step many people overlook. Each time a tyre is removed from the wheel, the sensor's rubber valve components are disturbed. Most manufacturers recommend fitting a fresh service kit, the valve core, seal, grommet, and nut, every time the tyre is changed, which usually costs only a few pounds per wheel.

Skipping this is a false economy. A perished valve seal can cause a slow leak that drains the very tyre the sensor is meant to protect. When you have new tyres fitted, it's worth asking whether the TPMS service kits are included in the price.

What we do at Park Royal Tyre & Alignment Centre

We treat TPMS as a routine part of every tyre job, not an afterthought. Our technicians use an electronic diagnostic check to read sensor IDs, programme replacement sensors, and reset both direct and indirect systems so the warning light clears correctly. We stock both vehicle-specific and programmable universal sensors to suit most makes and models.

When you visit us in Park Royal, we'll check sensor battery health, fit fresh valve service kits during tyre changes, and make sure your system is reading accurately before you drive away. If a sensor has reached the end of its life, we'll explain your options clearly without pressure.

Frequently asked questions

Can I keep driving with the TPMS light on?

You can drive, but you shouldn't ignore it. A steady light means a tyre is low and needs checking promptly, as underinflation raises blowout risk and fuel use. It's best to sort the fault out quickly to keep your tyres safe and your car road-legal.

How long do TPMS sensor batteries last?

Direct TPMS sensor batteries are sealed and typically last between five and ten years, depending on use and mileage. They can't be replaced individually, so the whole sensor is renewed when the battery dies. This is why older cars sometimes show a fault light with no actual pressure problem.

Does topping up the air always turn the light off?

Not always. On direct systems the light usually clears within a short drive once pressures are correct. Indirect systems normally need a manual reset through the dashboard menu. If the light persists after correct inflation, it usually points to a sensor or system fault rather than low pressure.

Are TPMS sensors required by law in the UK?

Sensors must be fitted and working on cars that were originally built with TPMS, which covers all new cars sold since November 2014. You can't legally remove or disable a working system, and a malfunctioning one can leave an eligible vehicle unroadworthy.

If your tyre pressure warning light is on, or you're due new tyres and want the TPMS handled properly, we're here to help. Call Park Royal Tyre & Alignment Centre on 020 3886 2355, message us on WhatsApp at 07476 586 589, or get in touch here to book a visit at NW10 7TR.