Do not wait for a small fault to become a roadside breakdown or a larger repair bill.
An engine management light or any other dashboard warning light.
Loss of power, hesitation or rough running
The car entering limp mode, or poor fuel economy you cannot explain
A second-hand car you are thinking of buying and want checked first
An amber warning light usually means the fault needs checking soon, so drive carefully and book a check. A red or flashing light, or a sudden loss of power, means stop somewhere safe and call for help.