Ignition
Worn spark plugs, a failing ignition coil or a damaged lead are the most common causes on petrol engines.
Air and fuel
Vacuum leaks, dirty injectors, a dirty throttle body or a faulty sensor can upset the mixture.
Mechanical
Low compression from valve or head gasket problems is less common but needs to be ruled out on a persistent misfire.
What to tell the mechanic
Whether the engine light is solid or flashing, when it happens (cold, idle, under load), and when plugs were last done.
Safe to drive?
A flashing check engine light means an active misfire that can damage the catalytic converter. Reduce load and book in promptly.
General guidance only, not a diagnosis. If in doubt, do not drive it and have it inspected. In an emergency, call 111.
Who can help
Get quotes for car diagnostics near you
Questions
Will a tune-up fix it?
Only if plugs or coils are the cause. Testing first saves money.
What should I put in the job?
Symptoms, warning lights and kilometres since the last service.