Check Engine light is on: what to check
LLCAR Editorial Team · updated
If the Check Engine light flashes while the engine is running or the engine shakes badly, stop in a safe place and seek assistance. If the light remains steadily lit, check your vehicle's manual and save the OBD-II code for diagnostics.
Why the light's behaviour matters
A flashing light can accompany severe misfires. In this condition the catalytic converter can be damaged. With a steady light, the course of action depends on the car model, any accompanying warnings and how the engine behaves.
If a red oil pressure or overheating warning is on at the same time, follow the manufacturer's guidance for that warning.
How to record an engine fault
- Check the car while parked. Connect a compatible Bluetooth OBD-II adapter following the instructions for your vehicle and the adapter.
- Open the fault codes in LLCAR and save the full code, time, mileage and the conditions when it appeared. If the scanner shows a freeze frame, save that too.
- Show the records to a specialist before clearing the codes. A reset may delete the data they would use to determine the cause.
Examples of OBD-II codes
- P0171 — fuel mixture too lean, bank 1.
- P0300 — random or multiple misfires.
- P0420 — catalytic converter efficiency below threshold, bank 1.
A code helps guide the initial checks. The repair decision is made after inspecting the vehicle.