Check Engine Light Flashing: What It Means and What to Do

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A steady check engine light means the car has found a fault and should be checked soon. A flashing check engine light is more serious: it usually signals an active engine misfire that can damage the catalytic converter. Here is what to do.

If the Light Is Flashing

  • Reduce speed and load, avoid heavy acceleration and towing.
  • Get somewhere safe and have the car checked as soon as you can.
  • If the car is shaking badly, losing power or smells of fuel, stop driving and get it towed.

What Usually Causes It

  • Worn spark plugs or ignition coils
  • A failing fuel injector
  • Vacuum leaks or other air problems
  • Sensor faults

If the Light Is Steady

A steady light is less urgent but should not be ignored. A loose or missing fuel cap is a common and cheap cause, so tighten it and drive for a while to see whether the light goes out.

Read the Code

An OBD2 scanner tells you which fault the computer has found. Misfire codes usually start with P030 (for example P0300 for a random misfire, or P0301 for cylinder 1). See my guide to common OBD2 error codes and my OBD2 scanner guide. If you need to clear a code afterwards, read how to clear OBD2 codes.