● Stop driving
Driving on can cause serious damage or leave the car stranded.
Driving on can cause serious damage or leave the car stranded.
The engine computer sees misfires on more than one cylinder or with no fixed pattern. The driver usually notices rough idle, shaking and weak acceleration, and the engine light may flash.
Guided check
- Is the engine light flashing?If yes: Stop driving and reduce load. A flashing light means unburnt fuel can damage the catalytic converter. Find the misfire before any road test.
- Does the misfire move when you swap the coil to another cylinder?If yes: The coil is the likely cause. Replace it and clear the code, then road test.
- Are the spark plugs worn, oily or wet?If yes: Replace the plugs. If they are oily or fuel wet, also find out why before finishing the job.
- Is the compression low on the misfiring cylinder?If yes: This is a mechanical problem such as valves, rings or head gasket. Do a leak-down test before ordering parts.
These checks are general and are still being reviewed by working mechanics.
Causes vary by car. Test before you order a part.
Likely causes, most common first
- Worn spark plugs or coils
- Vacuum leak or unmetered air
- Low fuel pressure or dirty injectors
- Low compression
Parts usually involved
- Spark plugs Find at suppliers
- Ignition coils Find at suppliers
- Fuel injectors Find at suppliers
- Intake gaskets Find at suppliers
Test before you replace
Read the misfire counters and fuel trims, then check for vacuum leaks and fuel pressure before replacing ignition parts.
General guidance for generic OBD2 codes. Always follow the maker's procedure for the car in front of you.