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Dashboard warning lights and the MOT: which ones mean a fail?
An engine, ABS or airbag light that stays on is a major defect at the MOT, even if the car drives perfectly. Which lights testers check, and what to do first.
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Modern cars use dashboard warning lights to report faults in their safety and emissions systems. Since the MOT changes of May 2018, the test checks many of these lights directly. A light showing a fault is often an automatic fail, even if the car seems to drive perfectly.
The lights a tester checks are listed below, with what each one means and what to do before you book.
How testers check warning lights
Most warning lights come on briefly when you switch the ignition on, as a self-check, then go out once the engine starts. The tester looks for two problems:
- A light that stays on, which means the system has detected a fault.
- A light that never comes on, which can mean the bulb has failed or the light has been disconnected to hide a fault.
Both can lead to a fail.
Warning lights that can fail an MOT
| Warning light | When it applies | Category |
|---|---|---|
| Engine malfunction (engine management) | Petrol cars first used from 1 July 2003, diesels from 1 July 2008 | Major |
| ABS (anti-lock brakes) | Cars fitted with ABS | Major |
| Electronic parking brake | Cars fitted with one | Major |
| Airbag / SRS | Cars fitted with airbags | Major |
| Electronic power steering | Cars fitted with EPS | Major |
| Tyre pressure monitoring | Passenger cars first used from 1 January 2012 | Major |
| Brake fluid level | Cars fitted with one | Minor |
A major defect is a fail, and the car needs repairing before it can pass. A minor defect doesn't stop a pass, but it's recorded on the certificate. Our guide to MOT defect categories explains the difference.
Check the latest rules
The lights explained
Engine management light
Usually an amber engine symbol. It can mean anything from a loose fuel cap to a failing sensor, catalytic converter or diesel particulate filter (DPF). Because it often relates to emissions, an engine fault can also cause the emissions test to fail. A garage with a diagnostic reader can tell you the stored fault code.
ABS light
Shows a fault in the anti-lock braking system, often a wheel speed sensor. The normal brakes still work, but the car won't prevent the wheels locking under hard braking. If the red brake warning light is on as well, get it checked before driving.
Airbag (SRS) light
Shows a fault in the airbags or seatbelt pre-tensioners. It may mean an airbag won't go off in a crash. Common causes include a damaged connector under a seat or a worn clock spring behind the steering wheel. A light only showing that the passenger airbag is switched off, for example for a rear-facing child seat, isn't a defect.
Power steering light
Shows a fault in the electric power steering. The car can usually still be steered, but it may be much heavier. Some faults are caused by a weak battery or low voltage, so it's worth checking the battery first.
Tyre pressure light
On cars from 2012 onwards, this light shows either low pressure or a fault in the monitoring system. Set the tyres to the right pressures and reset the system as the handbook describes. If the light flashes and then stays on, there's usually a system fault, such as a failed sensor. Our guide to tyre tread depth and the MOT covers the other tyre checks.
Brake fluid light
Low brake fluid can be a sign of worn brake pads or a leak. It's recorded as a minor defect, but it's worth investigating quickly because brake fluid doesn't normally go down on its own.
Check a car's MOT history for warning light failures
Official DVSA MOT records: MOT status, the latest test and its advisories. No sign-up.
What to do before the MOT
- Switch on the ignition and watch the dashboard. Note any light that stays on, or doesn't come on at all.
- Check the handbook. Some lights, such as the service reminder, have nothing to do with the MOT.
- Get a diagnostic check. Many garages and parts shops can read fault codes for a small fee, or for free.
- Fix the fault, not just the light. Clearing a code without fixing the cause rarely lasts until the test, and the fault may show up in other checks.
- Book the MOT early. Testing up to a month before expiry gives you time to fix a fail without losing your renewal date. See how early you can MOT a car.
Warning lights and used cars
When you're buying a used car, warning light failures in the MOT history are worth asking about. An airbag or ABS fail that was fixed straight away is fine. The same light failing year after year, or a recent fail with no pass afterwards, suggests a fault that's never been properly repaired.
Our MOT history check shows every past fail and advisory, and our guide to reading MOT history before buying explains what to look for.
One last check before the test
If a safety or engine warning light is on, assume it will fail the MOT. Find out what the fault is, fix it properly and check the dashboard again before the test. It's usually much cheaper than a fail and a retest.
Ready to check a vehicle?
Official DVSA MOT records: MOT status, the latest test and its advisories. No sign-up.