MOT / Roadworthiness Test — How to Prepare with an OBD2 Scanner

Failing a roadworthiness test because of an engine light means a lost appointment and a re-test to pay for again. An OBD2 scanner lets you anticipate this kind of bad surprise before you even book.

Why the engine light causes a fail

In Belgium, an engine light on at the time of the roadworthiness test generally results in a failure, unless the inspector judges it to be a clearly identified minor fault with no safety or environmental risk.

Checking your codes before the appointment

What not to do

The only reliable approach is to diagnose the real cause, repair it if needed, then allow time for the monitors to revalidate naturally before the appointment.

FAQ — Roadworthiness test

How long before the test should I check?

Ideally one to two weeks before, to have time to repair and drive enough kilometres if a code is detected.

Can a minor fault still pass the test?

Yes, some clearly identified minor faults can be accepted at the inspector's discretion — but this is never guaranteed in advance.

Does the roadworthiness test check anything beyond the engine?

Yes, the test covers many other aspects (brakes, lights, emissions, chassis) — the OBD2 scanner only covers the engine and related systems readable via the OBD2 standard.