A steady engine management light usually allows continued gentle driving to get the car checked soon, while a flashing engine management light indicates an active misfire and calls for stopping as soon as it's safely possible, since continuing can damage the catalytic converter.
A constantly illuminated (not flashing) engine management light typically indicates the engine computer has detected a fault outside its expected parameters — this could be anything from a loose fuel cap to a failing sensor. It's generally safe to continue driving carefully and have it checked within the next few days, though performance may be slightly reduced.
A flashing engine management light is a more urgent signal, usually indicating an active engine misfire. Continuing to drive with a genuine misfire can allow unburned fuel to reach and damage the catalytic converter — an expensive component to replace. If the light is flashing, reduce speed, avoid hard acceleration, and get to a safe place to stop as soon as reasonably possible.
Common causes range from something as simple as a loose or faulty fuel filler cap, to a failing oxygen sensor, a vacuum leak, worn spark plugs or ignition coils, or issues with emissions components like the EGR valve or catalytic converter.
The engine computer stores a specific fault code explaining what triggered the light, which can be read with a diagnostic scanner. This is by far the most direct way to identify the actual cause rather than guessing based on symptoms alone.
An illuminated engine management light is a guaranteed MOT failure in the UK, regardless of what specifically triggered it or how minor the underlying cause turns out to be. This makes it worth getting checked before a test is due, even if the car otherwise seems to be running fine.
Yes, a flashing light typically indicates an active misfire that can damage the catalytic converter if you keep driving normally, while a steady light usually allows continued careful driving to get it checked soon.
Yes, a loose or faulty fuel filler cap is one of the most common and easily fixed triggers, since it disrupts the evaporative emissions system the engine computer monitors.
A steady light should be checked within the next few days. A flashing light calls for stopping as soon as it's safely possible and arranging inspection or recovery rather than continuing the journey as normal.
MotorLoom analyses the symptoms you describe and points you toward the most likely cause in under a minute.
Get My Free Fault ScanLast reviewed 2026-09-08 by the MotorLoom editorial team.