Safety note: a flashing check engine light means an active misfire that can damage the catalytic converter and other parts. Stop driving as soon as it is safe and call for service.
Short answer
The most common causes of a check engine light are oxygen sensor faults, ignition coil or spark plug failure, EVAP system leaks (including a loose gas cap), mass airflow sensor issues, and catalytic converter problems. The exact cause needs to be confirmed with diagnostic testing because the same code can have several possible failure points.
Solid vs flashing
A solid check engine light means the computer found a problem important enough to log but not urgent enough to stop the vehicle. Schedule diagnostics soon.
A flashing check engine light usually means active misfire. Driving with an active misfire dumps unburned fuel into the catalytic converter and can destroy it in miles. Stop driving as soon as it is safe.
Common causes ranked
Oxygen sensor issues are common, especially as vehicles age. They affect fuel trim and emissions.
Ignition coil or spark plug failure causes misfire codes and can trigger a flashing light when active.
EVAP system leaks include loose gas caps, cracked hoses, and failed purge valves. They rarely affect drivability but they keep the light on.
Mass airflow sensor faults change fuel mixture and may make the vehicle run rough or stall.
Catalytic converter failure is often the result of unresolved misfires or oil-burning conditions.
What not to do
Do not clear the code and hope it goes away. Clearing erases freeze frame data the technician needs.
Do not assume the part the code names is the part that failed. AAB Service tests the system before replacing parts.
Do not skip an inspection appointment because the light went off on its own; the code is still stored.
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