Check engine light is flashing but then remains solid

Contents

What The Check Engine Error is Telling You

Flashing CEL: Signals a severe engine misfire, which can dump unburned fuel into the exhaust and damage the catalytic converter. Immediate attention is required.
Solid CEL: Indicates a stored trouble code (less urgent but still important). The issue may be intermittent or less severe.

Ignition System Failure (e.g., faulty spark plugs, ignition coils, or wires – accounts for ~60% of cases).
Fuel Delivery Problems (clogged fuel injector, weak fuel pump, or low pressure).
Exhaust System Issues (failed oxygen sensor or catalytic converter damage from prolonged misfires).
Vacuum Leaks (cracked hoses or intake manifold gasket leaks causing lean conditions).
Sensor/ECU Failures (rare but possible, e.g., crankshaft position sensor or ECU malfunction).

If the light flashed: Stop driving ASAP. Towing to a mechanic is safest to avoid catalytic converter damage.
If the light is solid: Drive cautiously and retrieve trouble codes. Many auto parts stores (e.g., AutoZone) offer free OBD-II scans.

Step 1: Retrieve Codes Use an OBD-II scanner to pull trouble codes. Example codes:

Code	Probable Cause	Fix
P0300	Random misfire	Check spark plugs, coils, fuel system
P0172	Rich fuel mixture	Inspect oxygen sensors, fuel pressure

Step 2: Perform Tests Based on codes:
- Ignition: Check spark plugs/coils with a multimeter.
- Fuel: Test pressure at the rail; inspect injectors.
- Compression: Perform a compression test if misfires persist.

Common Fixes & Costs:
- Spark plugs: $50–$150 (DIY or pro).
- Ignition coil: $150–$300 (parts + labor).
- Catalytic converter: $1,000+ if damaged.
DIY vs. Pro: Replacing plugs/coils is often DIY-friendly; fuel/exhaust repairs typically need a mechanic.

Replace spark plugs per manufacturer intervals (typically 30,000–100,000 miles).
Use quality fuel and injector cleaner periodically.
Address minor CELs promptly to avoid cascading damage.