Random/Multiple Cylinder Misfire Detected
The air and fuel mixture is not burning properly in several cylinders, or the engine computer detects misfires but cannot tell which cylinder. It notices because the crankshaft (the shaft the pistons turn) slows down for an instant at every failed combustion.
What the car has detected
The engine computer has counted more failed combustions than it allows, spread across several cylinders or impossible to pin on a single one. It may appear alone or together with cylinder-specific codes (P0301, P0302…).
A misfire can damage the catalytic converter. If the warning light flashes, drive as little as possible. Stop if the engine shakes badly, loses a lot of power, overheats, makes unusual noises or smells strongly of fuel.
Symptoms
- Engine warning light on or flashing
- Rough idle or vibration
- Hesitation and poor acceleration
- Higher fuel consumption
- Strong fuel smell from the exhaust
- Misfires only when cold, while warming up or under load
Possible causes
- Ignition coils, spark plugs or leads, sometimes several at once
- Dirty or leaking injectors, weak pump, clogged filter or bad fuel
- Air leaks, or a mass air flow or oxygen sensor giving wrong readings
- Crankshaft or camshaft sensors
- Weak battery or low charging voltage
- Mechanical problems: valves, head gasket or low compression
- Outdated engine computer software
Checks for the garage
- Read all the codes (pending ones too) and save the freeze frame data before clearing
- Look at each cylinder's misfire counters and the conditions in which they rise
- Check battery and charging voltage
- Test the coils and connectors and inspect the spark plugs
- Look for air leaks using the fuel trims and a smoke test
- Test fuel pressure, volume and injectors, and do a compression test if the misfires concentrate on one cylinder
- Check the manufacturer's technical bulletins and software updates
Next step
Note when it misfires (cold, at idle or under load) and have the ignition, fuel system and air leaks checked.
Go to a garage as soon as possible: when several cylinders misfire, the cause is usually something they share (fuel, air, voltage or sensors) and diagnostic equipment is needed. If the light flashes, the car shakes badly or loses power, drive as little as possible.