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What Is TPMS? A Complete Guide to Tyre Pressure Monitoring Systems

That little horseshoe-shaped warning light catches drivers out every day. Here's what your TPMS is telling you, why it matters for your MOT, and exactly what to do when it appears.

Updated July 20267 min read

TPMS: the essentials

  • Mandatory on all new cars sold in the UK and EU since November 2014
  • A faulty or illuminated TPMS has been an MOT failure since 2015 (for cars first used from January 2012)
  • The warning light usually triggers when a tyre is around 25% underinflated
  • Two types exist: direct (a sensor in each wheel) and indirect (via the ABS system)

What is TPMS?

TPMS stands for Tyre Pressure Monitoring System. It's an electronic system that keeps an eye on your tyre pressures and warns you - via a dashboard light - if one drops too low. Underinflated tyres are dangerous: they reduce grip and braking, wear out faster, increase fuel consumption and can overheat and fail.

Why is my TPMS light on?

A TPMS warning can mean several things:

  • One or more tyres are underinflated - often by around 25% or more
  • A slow puncture is letting pressure down gradually
  • A cold snap - pressures drop as the temperature falls
  • A sensor fault or flat sensor battery
  • The system hasn't been reset after new tyres or a pressure change

If the light flashes when you start up and then stays on, that usually points to a system fault rather than a soft tyre - worth getting checked.

Direct vs indirect TPMS

Direct TPMS

Direct systems use a battery-powered sensor inside each wheel that measures the actual pressure and sends it to the car. Accurate, but the sensors have a finite battery life and need attention when you change tyres.

Indirect TPMS

Indirect systems don't measure pressure directly. Instead they use the ABS wheel-speed sensors: an underinflated tyre is slightly smaller and spins a little faster, which the system detects. There's no sensor to replace, but it must be reset after inflating or changing tyres.

Is TPMS a legal requirement?

Yes. TPMS has been mandatory on all new cars sold in the UK and EU since November 2014, and it became part of the MOT test in 2015 for vehicles first used on or after 1 January 2012. If the TPMS warning light is illuminated at the MOT, it's an automatic fail - so it's not something to ignore.

“People panic when the light comes on, but nine times out of ten it's just a soft tyre or a slow puncture. The bit that catches drivers out is the MOT - if that light's on, it's an automatic fail. We can check your pressures, sort a puncture and reset or replace a sensor right at your door.”

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Aaron Duncan
Owner, Grangetown Tyres

What to do when the light comes on

  1. Check your tyre pressures when the tyres are cold, using the figures in your handbook or door pillar
  2. Inflate any low tyres to the correct pressure
  3. Look for obvious signs of a puncture - a nail, a bulge, or a tyre going down again
  4. If the light stays on after correcting pressures, get the system checked

TPMS and new tyres

When you have new tyres fitted on a direct system, the sensors need to be handled with care and the system reset, cloned or - if a sensor battery has died - replaced. Direct sensor batteries typically last around 5-10 years. A good mobile fitter will check and reset your TPMS as part of the job.

Why correct pressure matters

Keeping your tyres at the right pressure isn't just about the warning light. Correct pressures mean shorter braking distances and better grip, lower fuel bills, longer tyre life and more even wear. TPMS is simply there to help you stay on top of it.

Frequently asked questions

Does a TPMS light mean I have a puncture?

Not always. It means at least one tyre is low on pressure - which could be a slow puncture, a temperature drop, or simply a tyre that needs topping up. Check your pressures and inspect for damage.

Will a TPMS warning fail my MOT?

Yes. Since 2015, an illuminated or faulty TPMS is an automatic MOT failure for cars first used on or after 1 January 2012.

How long do TPMS sensors last?

Direct TPMS sensor batteries typically last around 5-10 years, after which the sensor usually needs replacing.

Do I need to reset TPMS after fitting new tyres?

Yes. The system should be reset - and on direct systems the sensors checked or replaced - whenever tyres are changed.

Can a mobile tyre fitter sort my TPMS?

Yes. We can check pressures, repair punctures, and reset or replace TPMS sensors at your home or work.

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