P0303Powertrain
Powertrain · SAE
Cylinder 3 misfire detected
Meaning
The control unit detects misfires concentrated on cylinder 3 rather than spread across the other cylinders. Combustion in that cylinder is irregular or absent.
Common causes
- Cylinder 3 spark plug worn, fouled or with damaged electrodes
- Faulty ignition coil or plug lead on cylinder 3
- Cylinder 3 injector clogged, stuck or electrically failed
- Low compression on cylinder 3 (valves, piston rings or head gasket)
- Poor electrical connection in the cylinder 3 ignition circuit
- Localized air leak or faulty intake manifold gasket
Symptoms
- Rough running and vibration, especially at idle
- Check-engine light on or flashing
- Loss of power and hesitant acceleration
- Higher fuel consumption and smell of unburned fuel
- Hard cold starting
Severity
Serious: if the light is flashing, stop driving, because unburned fuel reaching the catalytic converter can overheat and destroy it.
What to do
- Read the freeze-frame data and misfire counters to confirm the fault is isolated to cylinder 3
- Swap the cylinder 3 coil and spark plug to another cylinder and check whether the misfire follows the moved part
- Check the cylinder 3 injector (resistance, drive signal and flow) and inspect the wiring
- If plug, coil and injector are sound, perform a compression test on cylinder 3