Question of the week: Is a warning light on the dashboard an MoT fail?

David Ross, Editor
Fri, 25 Oct 2024

Dear Honest John,

"Would a faulty stop-start system mean an MoT fail? The light is currently on. And what other dashboard lights would mean an MoT fail?"

- CD

Dear CD,

MoT time can be a stressful experience, particularly if your car is otherwise faultless but you get a pesky warning light show up without much time to solve the cause.

As a general rule, a warning light in the instrument display will be a fail point if it indicates the failure of a component that is also part of the test procedure. For example, an ABS warning light or headlight main beam  warning that is illuminated likely means that those systems are not functioning correctly, which would also mean a fail.

Unfortunately the MoT inspection manual doesn't provide a comprehensive list of warning lights that would cause a failure. An engine management warning light being can also be a fail, because although the car may appear to be driving without issue, it could mean its emissions aren't where they should be.

To further complicate matters an airbag warning light isn't necessarily a failure. As the MoT inspection manual says, 'The SRS MIL (Malfunction Indicator Lamp) should only be failed if it is indicating a system malfunction. A lamp illuminated to indicate the passenger airbag is disabled is not to be regarded as a defect.

Warning messages on dashboard displays are not a defect in their own right, but may assist the tester in determining that the warning lamp is illuminated because a malfunction exists.'

If your stop-start system isn't working it is unlikely to be a failure, because it's not a safety critical system and doesn't stop the car from working as it should - it's a feature you can turn off anyway - but that doesn't guarantee a particularly harsh MoT tester won't mark it down as a defect.

Ask HJ

Will my car fail its MoT for non-working blind spot warning?

My car has developed a fault in that the Active Blind Spot system which is not working. Living in a rural part of Scotland this is no great concern however the car is due an MoT shortly and wonder if this is likely to cause a failure?

It is not a certainty that this system being out of action will result in an MoT failure, as it is not on the list of safety-critical functions such as the braking system, airbag or engine management system which would be an automatic failure. It may depend on how the warning is displayed in the instrument panel, as red warnings are typically an automatic fail while amber warnings may be failed depending on which component it relates to.

Answered by David Ross

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