Ignition and Misfire Codes

Codes for misfires, ignition coils, spark plugs and the crankshaft and camshaft position sensors, which the computer needs to know when to inject fuel and when to fire the spark.

The computer detects misfires by measuring tiny changes in crankshaft speed. When the misfire is severe, the check engine light flashes: unburned fuel reaches the catalytic converter and can damage it within minutes.

Most searched codes in this system

• P0300: random or multiple-cylinder misfire.
• P0301 to P0308: misfire in a specific cylinder.
• P0335 to P0339: crankshaft position sensor.
• P0340 to P0344: camshaft position sensor.
• P0351 to P0358: primary circuit of each ignition coil.

What to check first

1. If the light is flashing, reduce the load and stop as soon as it is safe.
2. Swap the coil from the affected cylinder with another one and see whether the misfire moves.
3. Check the condition and gap of the spark plugs.
4. If several cylinders misfire, think of common causes: vacuum leaks, fuel delivery or compression.