A tyre pressure monitoring system, or TPMS, is the technology behind the tyre pressure warning light on your dashboard. Its job is simple, which is to keep an eye on the air in your tyres and warn you the moment one runs low. Most of us only notice it when the light appears, but it is quietly doing its job every time you drive.
It is now fitted to almost every car on the road, yet many drivers are not sure how it works or what to do when the light appears. Understanding the basics takes only a few minutes, and it can save you from a breakdown or a failed MOT.
What is a Tyre Pressure Monitoring System (TPMS)?
A TPMS is an electronic system that monitors the air pressure in your tyres while you drive. When a tyre drops below a safe level, usually around 20% under the recommended pressure, it switches on a warning light on your dashboard. Tyres lose a little air naturally over time, and a slow puncture or cold weather can speed that up, which is when the warning matters most.
That warning light is a small horseshoe shape with an exclamation mark in the middle, designed to look like a cross-section of a tyre. It is easy to miss if you do not know what you are looking for.
TPMS is not just a convenience, either. It is fitted to almost every modern car, and on vehicles first used from January 2012, the system has to be working for the car to pass its MOT. In short, if your car is from the last decade or so, it almost certainly has TPMS, and a fault can mean a failed test.
How Does a TPMS Work?
Every TPMS has the same goal, which is to warn you about a low tyre before it turns into a problem. There are two ways it can do this, known as direct and indirect, and they work quite differently.
Direct TPMS
A direct system uses a small sensor fitted inside each wheel, usually on the valve. These sensors measure the actual air pressure in every tyre, and many also read the temperature. Because the reading comes straight from inside the tyre, the system reacts quickly to a sudden drop in pressure.
The sensors then send their readings wirelessly to the car’s computer. If the pressure in any tyre falls too low, the computer turns on the warning light, and on many cars, it can show you the exact pressure in each tyre. This makes direct systems accurate and quick to flag a problem.
Indirect TPMS
An indirect system has no pressure sensors at all. Instead, it borrows the wheel-speed sensors that the car already uses for its anti-lock brakes. This keeps it cheaper to build, as there is no extra hardware to fit inside the wheels.
The system relies on a simple principle. A tyre that loses pressure changes its rolling characteristics, which the system detects by monitoring wheel-speed data from the ABS sensors. When the system detects one wheel turning faster than the rest, it treats that tyre as under-inflated and switches on the warning light. This approach is simpler and cheaper than a direct system, but it cannot tell you the exact pressure.
Direct vs. Indirect TPMS: What’s the Difference?
Both systems do the same job, but each has its strengths. The main differences come down to four things:
Accuracy
Direct systems show the real pressure in each tyre, and many display the exact figure on the dashboard. In contrast, indirect systems only estimate pressure from wheel speed, so they are less precise and cannot give you an actual reading.
Cost
Indirect systems are the cheaper option because they rely on the ABS sensors the car already has. Direct systems cost more, as they need a separate sensor fitted in every wheel.
Resetting After a Tyre Change
Indirect systems usually need resetting or recalibrating whenever you inflate or change a tyre. Direct systems update on their own, so there is less for you to remember.
Upkeep
Direct sensors run on small batteries that last around five to seven years, and they can be damaged during a tyre change. Whereas indirect systems have no sensors of their own, so there is nothing extra to fail.
Neither type is better in every situation. Direct TPMS gives you more detail, indirect TPMS keeps things simple and low cost, and your car’s handbook will tell you which one you have.
Got a Warning You Cannot Clear?
Whichever system your car uses, a TPMS can only flag a problem, not fix it. If a warning keeps returning, the cause is usually a slow puncture or a tyre that has reached the end of its life, and that needs hands on the wheel rather than another reset. Mobile Tyre Local handles exactly that, bringing the tools and replacement tyres to wherever you are parked.
Ring 07731306351 and a fitter can be on the way.
What to Do When Your TPMS Warning Light Comes On?
A TPMS light is easy to ignore, but it is worth acting on straight away. Your tyres are your only contact with the road, and with 29,711 people killed or seriously injured on Britain’s roads in 2023, anything that affects your grip and braking deserves attention. Even a tyre that looks fine can be low enough to affect how the car handles, so the warning is worth trusting.
If the light comes on, here is what to do:
- Find a safe place to slow down and stop, rather than braking sharply.
- Check the pressure in all four tyres with an accurate gauge once they are cold.
- Inflate any low tyres to the pressure listed in your handbook or on the door sill.
- Look for an obvious cause, such as a nail, a bulge or a cut in the tyre.
If a tyre keeps losing air after you have inflated it, you most likely have a puncture or damage that needs a professional to repair or replace. Acting quickly keeps you safe and stops a small problem from turning into a blowout.
Does a TPMS Replace Checking Your Tyres Yourself?
No. A TPMS is a useful safety net, but it is not a substitute for checking your tyres by hand. It is built to catch a problem once it has already developed, not to keep your tyres in good shape day to day.
There are a few reasons it cannot do the job on its own:
- It warns you late: The light only comes on once a tyre is already well under-inflated, by which point you have lost some grip and fuel economy.
- It can miss a slow, even drop: An indirect system may not notice a problem if all four tyres lose air gradually and evenly.
- Tyre faults slip through unnoticed: DVSA figures show more than 2.1 million vehicles failed their MOT on tyre defects in 2023-24, many of them problems a quick manual check would have caught.
The safest habit is to check your tyres yourself about once a month, and before any long journey. A quick look at the pressure, tread and general condition takes only minutes, and it catches the problems a warning light can leave too late.
Important FAQs
What does the TPMS warning light mean?
The TPMS light, a horseshoe shape with an exclamation mark, means one or more of your tyres is low on pressure. You should check all four tyres and inflate any that are below the recommended level as soon as it is safe to do so.
Can I drive with the TPMS light on?
You can drive a short distance to a safe place to check or inflate your tyres, but you should not ignore it. A low tyre affects your grip and braking and can fail if you keep driving on it.
Why is my TPMS light still on after inflating my tyres?
Some systems, especially indirect ones, need to be reset or recalibrated after you adjust the pressure. Check your handbook for the reset process, and if the light stays on, have the system checked in case a sensor has failed.
How long do TPMS sensors last?
The sensors in a direct system run on small batteries that usually last around five to seven years. When a battery runs out, the whole sensor normally needs replacing, which is often done when you change the tyre.
Does a TPMS replace checking my tyres manually?
No, a TPMS is a useful safety net, but it only warns you once a tyre is already low. Checking your tyres by hand once a month is still the best way to catch problems early.
Bottom Line
A tyre pressure monitoring system is a simple but valuable safety feature, watching your tyres and warning you the moment one runs low. The key is to treat the warning light as a prompt to act, not something to put off. Pair it with a quick manual check each month, and you will keep your tyres safer, your fuel costs lower, and your car ready for the road.
A flat or failing tyre rarely waits for a convenient moment. When your needs attention, our mobile fitters at Mobile Tyre Local come to you at home, at work or at the roadside, with tyre repairs and replacements at fair prices, any hour of the day and every day of the week.
Call our experts to book your callout, and we will take care of the rest.
