How to Clear Dashboard Warning Lights Before Your MOT

Since the MOT rule changes introduced in recent years, the DVSA has taken a much stricter stance on dashboard warning lights. In the past, some warning lights might have only generated an advisory, but today, an illuminated engine management light, ABS warning, airbag light, or TPMS indicator is an instant MOT failure.

If your car is displaying a dashboard warning light, you cannot simply ignore it or cover it with black tape. The MOT tester will turn the ignition on to ensure all the warning lights illuminate (to check the bulbs are working) and then go out once the engine starts. Here is exactly what you need to do to diagnose and clear these lights before your test.

Understanding the Colours

Dashboard warning lights use a traffic light colour system:

• Green or Blue: System is on and functioning normally (e.g., headlights or cruise control).
• Yellow or Amber: Indicates a fault has been detected. The car is usually still safe to drive, but it requires investigation soon. This will fail an MOT.
• Red: A serious or critical fault. Stop driving immediately and seek recovery. This will definitely fail an MOT and is unsafe.

1. The Engine Management Light (Check Engine Light)

The Engine Management Light (EML) can illuminate for dozens of reasons, ranging from a loose petrol cap to a failing catalytic converter or oxygen sensor. Because modern engines are complex, you cannot guess the cause.

How to clear it: You need an OBD2 (On-Board Diagnostics) scanner. This simple device plugs into a port usually located under the driver's side dashboard. It will read the specific fault code (e.g., P0420) stored by the car's computer, telling you exactly what is wrong. Once the underlying issue is repaired, the scanner can be used to clear the code and turn the light off.

2. The ABS (Anti-lock Braking System) Light

The ABS prevents your wheels from locking up during emergency braking. If this light is on, the ABS system is disabled, though normal braking usually still works. Common causes include a dirty or faulty wheel speed sensor, low brake fluid, or a damaged ABS ring.

How to clear it: Check your brake fluid level first. If it's fine, the most likely culprit is a wheel speed sensor. An advanced OBD2 scanner can tell you exactly which wheel is registering a fault. The sensor can often be cleaned or replaced relatively cheaply.

3. The Airbag / SRS Light

An illuminated airbag light means the car's Supplemental Restraint System has detected a fault, and the airbags may not deploy in a crash. This is a major safety issue and an immediate MOT fail.

How to clear it: A very common cause for this is a loose connector under the front seats (often disturbed when vacuuming or moving the seat). Check the wiring plugs under the driver and passenger seats to ensure they are secure. Note: Standard cheap OBD2 scanners often cannot read airbag codes; you may need a more advanced scanner or a trip to a garage.

4. The TPMS (Tyre Pressure Monitoring System) Light

For cars registered after January 1, 2012, a faulty TPMS system is an MOT failure. The light usually comes on when a tyre drops below the recommended pressure, but it can also flash if a sensor battery has died.

How to clear it: Check the pressures of all four tyres (and the spare, if fitted) and inflate them to the correct PSI. Once inflated, you may need to reset the system via the car's infotainment screen or a button on the dashboard. If the light flashes, a TPMS sensor inside one of the wheels likely needs replacing by a tyre fitter.

Important Warning

Do not attempt to pass an MOT by removing the bulb behind the warning light in the dashboard. The MOT tester is trained to look for the light illuminating briefly when the ignition is turned on. If the light fails to illuminate during the start-up sequence, the car will still fail the test.

By diagnosing and repairing the root cause of these warning lights ahead of time, you will ensure a smoother, cheaper MOT experience.