Is Clearing Fault Codes Before An Mot Illegal Uk

Direct answer: clearing fault codes is not a magic legal loophole. This guide does not claim that pressing clear on a scanner is automatically a criminal offence. The practical MOT issue is simpler: if the fault is not repaired and the engine MIL or emissions warning indicates a malfunction on test day, the car can fail.

Illegal is the wrong first question

Drivers usually ask this when they really mean, "Can I clear the light and get through the MOT?" That is the risky part. Clearing stored codes does not repair a sensor, wiring fault, misfire, catalyst issue, DPF/SCR problem or air leak. If the ECU sees the fault again, the light can return.

What the MOT tester sees

The GOV.UK MOT manual tells testers to check the engine malfunction indicator lamp on relevant vehicles and lists an engine MIL that is inoperative or indicating a malfunction as a Major defect in the official MOT nuisance and emissions manual.

So the pass/fail problem is not whether a code existed yesterday. It is whether the vehicle arrives with the required warning-lamp behaviour and emissions condition today.

Why a fresh clear can backfire

• The same fault may return during the drive to the test centre.
• Readiness monitors may be incomplete after a reset.
• You lose freeze-frame evidence that could help the garage diagnose the cause.
• A permanent code may remain even when a dashboard light is temporarily off.

UK service-centre guidance warns against deleting an EML as a substitute for repair in this guide to clearing an EML before MOT. Another diagnostics guide explains why clearing shortly before MOT can create readiness problems; see Medway Vehicle Services on clearing fault codes.

Safe order before an MOT

1. Scan and save stored codes, pending codes, freeze-frame and readiness.
2. Repair or diagnose the underlying cause.
3. Clear codes only after the evidence is saved and the repair step is complete.
4. Drive normally until readiness monitors have completed where applicable.
5. Rescan and confirm the engine MIL is off before the MOT.

When not to proceed

Do not present the car as "fixed" just because the light is off after a reset. Stop and book help if the light flashes, the engine runs badly, a diesel has DPF/AdBlue countdown messages, or the same code returns after one drive.

Next step if you want to check before booking

If you want to record codes and readiness before deciding on a garage visit, check whether a scanner is suitable for your vehicle on the TOPDON CarPal product page. If the MOT is imminent and a warning lamp is on, book diagnosis rather than chasing resets.

FAQ

Can a garage tell I cleared codes?

They may see clues such as incomplete readiness, missing freeze-frame history or a fault that quickly returns. The bigger issue is that the cause is still present.

Is clearing codes ever OK?

Yes, after recording evidence and completing a repair, clearing codes can be part of verification. It should not be used to hide an unrepaired fault.