Written by the fitting team at 24/7 Mobile Tyre Services, Glasgow. Last reviewed: July 2026.
You have just fed a pound coin into an air machine in Govan. All four tyres set correctly. Back in the car, engine on, and the light is still sitting there.
Here is the reframe that helps. The light may not be reporting your tyre pressure any more. It may be reporting itself.
There is a ten second test that tells you which, and you can do it on the next start.
Quick answer: Watch the light when you start the engine. If it flashes for around a minute and then stays on, that indicates a fault in the monitoring system, usually a sensor at the end of its battery life or one that has not been registered to the car. If it comes on solid from the start, the system still believes a tyre is under inflated.
The ten second test: flashing or solid?
| What the light does | What it means | What to do |
|---|---|---|
| Flashes for roughly 60 to 90 seconds, then goes solid | System fault. Not a pressure problem | Adding more air will not help. Go to the fault section |
| Comes on solid from the start | The system thinks a tyre is low | Work through the pressure checks below |
That behaviour is defined by the standard these systems are built to, so it is broadly consistent across most makes, and it lines up with gov.uk’s guidance on TPMS.
Confirm it against your handbook though. Manufacturers vary in how they display faults, and some use a separate text message or a different amber warning entirely.
Which system does your car have? This matters enormously
Most articles on this topic assume every car has sensors in the wheels. Plenty do not, and that single assumption is why most of this content fails people.
Direct TPMS. A battery powered sensor inside each wheel, usually built into the valve, transmitting the actual measured pressure. Some cars display a live pressure per wheel on the dash.
These sensors are consumable items and need a service kit at every tyre change.
Indirect TPMS. No sensors in the wheels at all.
The car compares wheel speeds through the ABS system. An under inflated tyre has a slightly smaller rolling radius, so it turns marginally faster than the others, and the system spots the difference.
Cheaper, less precise, and it must be reset manually after any inflation, tyre change or rotation.
How to tell which you have:
- Does the dash show individual per wheel pressures? Almost certainly direct
- Is there a “reset” or “TPMS” button, or a tyre pressure item in the settings menu? Very likely indirect
- Your handbook settles it in thirty seconds
Why this decides everything. On an indirect system, no sensor can fail, because there are none. Any quote for sensors on an indirect system is a quote for parts your car does not have.
That is a sale we would rather not make, and it is worth ten seconds of your time to rule out.
If the light is solid: work through these first
- Check all four again with your own gauge, cold. Forecourt machines are frequently inaccurate and often read several PSI out, per TyreSafe’s pressure guidance. See why a tyre keeps losing air
- Use the right target figure. The door pillar plate, fuel flap sticker or handbook. Not the maximum moulded into the sidewall
- Check the spare. A small number of vehicles monitor the spare too. Rare in the UK, but it costs ten seconds
- Drive it. Many systems need a few minutes above roughly 15 to 25 mph before the sensors report in and the light clears. Sitting on the driveway will not do it
- Do the reset if the car has one. Indirect systems almost always require it. Some direct systems do too after a change
- Consider the temperature. A frosty morning drops pressures by several PSI. If the light comes on cold and clears as the tyres warm, your pressures are simply set a little low for the season
If the light flashed first: the four real causes
1. Sensor battery at end of life.
The battery is sealed inside the sensor. It is not replaceable, so the sensor itself is replaced.
Typical service life is somewhere in the range of five to ten years, which is why this tends to appear on cars around the seven to ten year mark.
Here is the honest pattern: they fail one at a time. People often end up replacing a second one within a year of the first. Some owners choose to change all four at once when the first goes, to save repeat labour. Both are reasonable positions, and it is your call.
The useful reframe: this is a wear item reaching end of life, not a fault with your car.
2. A sensor that has not been registered to the car.
After new wheels, winter wheels, a swap or a rotation, the system may need a relearn. That is automatic after a drive on some cars, an OBD relearn with a tool on others, or a fixed manual sequence on others again — most sensor makers publish a technical relearn overview that explains the general principle, though model specific steps stay with your handbook.
If the light appeared immediately after wheel work, this is very likely your cause, and it is a small job.
3. A damaged sensor. They break during careless fitting, in a pothole strike, or from over tightening the retaining nut same over torquing that turns up as a seized or rounded wheel nut elsewhere on the car.
Tyre sealant is a well known sensor killer. If you have used a sealant kit, say so when booking. See what to do when your spare is also flat.
4. Wheels without sensors. Winter or budget alloys fitted without sensors, or a steel spare in place. The system reports what it cannot find.
Rarer causes: a faulty receiver module, corrosion at the sensor’s valve base, or aftermarket electronics causing interference. That is workshop territory.
The MOT consequence: this is a deadline, not a nuisance
For vehicles first used on or after 1 January 2012, TPMS is an MOT item.
A system that is inoperative, or that has a warning lamp indicating a fault, is a major defect, and the vehicle fails.
That single fact converts an ignorable dashboard light into a dated job. If your MOT is next month, sort it now.
There is also a useful angle for anyone who has already failed. TPMS sits within the wheels and tyres group, which affects your retest timing. We explain that in what to do when your car fails the MOT on tyres.
Cars first used before that date are not caught by the rule. The light still means you have lost a safety system.
Can you just ignore it?
Legally, on a pre 2012 car, yes. Sensibly, no. Here is why, in terms that actually land.
TPMS typically only warns at around 25 percent below the recommended pressure. That is a long way down, and a lot of damage happens on the way there.
With the system inoperative, you lose the one thing that would tell you about a slow leak between manual checks.
And under inflation is not a small problem. It ruins fuel economy, wears the shoulders unevenly, lengthens wet stopping distances, and can overheat a sidewall into permanent internal damage. That turns a repairable tyre into a scrap one.
The honest bottom line: a TPMS light is a reason to check your pressures manually every couple of weeks until it is fixed. It is not a reason to stop thinking about your tyres.
Getting it fixed: what should happen, and what to ask
Diagnosis comes first. A TPMS tool reads each sensor’s ID, battery status and reported pressure at the wheel, in a couple of minutes, without the tyres coming off.
Any quote given without that read is a guess.
Replacement, done properly: the tyre is dismounted, the old sensor removed, the new one fitted and torqued to specification, the wheel resealed, rebalanced, and the sensor programmed and relearned to the car.
Programmable versus OE sensors:
| Type | Cost | Notes |
|---|---|---|
| Programmable universal | Cheaper | Covers most vehicles. Must still be relearned |
| OE sensor | Dearer | Matched to the vehicle. Must still be relearned |
Both are legitimate choices, and a fitter should offer you both.
Three questions worth asking:
- Was the system read with a tool before quoting?
- Is a new service kit included?
- Will the sensors be relearned to the car before I drive away?
The point that quietly matters most. A new service kit at every tyre change, meaning grommet, nut, core and cap, is the cheapest part of the whole job.
Skipping it is how a perfectly healthy sensor becomes a slow leak six months later. More on that in why a new tyre keeps losing air.
A pattern we notice
TPMS work arrives in clusters, and it is age driven rather than random.
Cars come to us around the eight year mark with one sensor gone. We read the system and the other three are usually reporting low battery status too, just not low enough to have triggered the lamp yet.
That read is the useful part of the conversation. It lets a customer decide whether to do one now and expect the next, or do all four while the tyres are already off the wheels.
Neither answer is wrong. What is wrong is quoting for four before anybody has read the system.
FAQs
Why is my tyre pressure light still on after inflating? Either the system has a fault rather than a pressure problem, or the car needs a reset or a short drive before it clears. Watch whether the light flashes on startup: flashing then solid points to a system fault.
What does a flashing TPMS light mean? On most systems, flashing for around 60 to 90 seconds and then staying solid indicates a fault in the monitoring system itself, such as a failed sensor or one that has not been registered to the car.
How long do TPMS sensors last? The sealed battery typically gives somewhere between five and ten years of service, depending on the sensor and how much the car is driven. They cannot be recharged or replaced individually.
Can you replace a TPMS sensor battery? No. The battery is sealed inside the sensor housing. When it reaches end of life, the sensor is replaced.
Does the TPMS light fail the MOT? For vehicles first used on or after 1 January 2012, yes. An inoperative system, or a warning lamp indicating a fault, is a major defect and the vehicle fails.
How do I reset my tyre pressure light? It depends entirely on the vehicle. Some reset automatically after a short drive, some have a button or menu item, and some need an OBD tool. Check your handbook for the correct procedure for your model year.
Do I need TPMS sensors in my winter wheels? On a direct TPMS car, yes, if you want the system to work and the light to stay off. Sensors also need relearning to the car when the wheels are swapped over.
Does tyre sealant damage TPMS sensors? It can. Sealant coats the sensor and can block the pressure port. If you have used a sealant kit, tell your fitter so the wheel and sensor can be cleaned properly.
If the light will not clear
We can read the system at your car, tell you which sensor is at fault, or whether your car even has sensors, and replace and relearn it there.
No garage trip. And no quote until we have actually read it.
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Related: TPMS sensor replacement in Glasgow, mobile tyre fitting, puncture repair, wheel balancing. Also relevant: pothole damage to two tyres and alloy wheels leaking around the bead.
