Check Engine — engine malfunction
The amber engine icon (Check Engine, MIL) is the universal OBD-II signal that the ECU detected a deviation in engine or related-system operation. The lamp does not identify a specific fault — it prompts you to read the DTC and investigate.
What this indicator means
The stylised engine outline lights up when the electronic control unit detects out-of-range parameters: misfires, abnormal air/fuel mixture, oxygen-sensor failures, EVAP-system leaks and dozens of other scenarios. Steady illumination marks a recorded fault that can be diagnosed; flashing warns of active catalytic-converter damage (misfires) — stop and reduce load immediately.
Common causes
- Misfires in one or more cylinders (P0300–P0308)
- Catalyst below efficiency threshold (P0420, P0430)
- Loose fuel cap or EVAP leak (P0440–P0457)
- Oxygen sensor, MAF or MAP failure
- EGR/DPF issues (on diesel engines)
- Abnormal air/fuel ratio (P0171, P0172)
What to do as a driver
Read the code via an OBD-II adapter (ELM327) and the Car Diagnostics app — the code will identify which subsystem is affected. If the lamp is flashing, immediately reduce load and pull over; otherwise you risk killing the catalyst. Steady illumination allows you to continue driving calmly to a workshop.
Safety
Flashing — critical: reduce revs and pull off the motorway. Steady — important: diagnose in the coming days.