Cylinder 5 Misfire Detected
What it means
The ECM measures crankshaft acceleration after each firing event via the crankshaft position sensor. When cylinder 5 repeatedly fails to accelerate the crank as expected, the misfire counter exceeds the threshold and P0305 is stored. If the misfire rate is high enough to damage the catalytic converter, the check engine light flashes. The cause can be ignition, fuel or mechanical and must be narrowed down.
Symptoms
- Check engine light steady or flashing under load
- Rough idle, shaking felt through the steering wheel and seat
- Stumble or jerking during acceleration, especially cold or under load
- Loss of power and increased fuel consumption
- Rotten-egg or raw fuel smell from the exhaust
Common causes
- Worn or fouled spark plug on cylinder 5
- Failed ignition coil or coil-on-plug boot with carbon tracking
- Clogged or electrically weak fuel injector on cylinder 5
- Vacuum leak at the intake manifold gasket near cylinder 5 (common on V6/V8 rear banks)
- Low compression: burnt exhaust valve, worn rings or head gasket leak
- Carbon buildup on intake valves (direct injection engines) or a sticking valve lifter
How to diagnose
- Read freeze frame: note rpm, load and coolant temperature when the misfire occurred. Check mode 6 data for cylinder 5 misfire counts versus the others.
- Pull the cylinder 5 spark plug: check gap (typically 0.8-1.1 mm), electrode wear, oil or fuel fouling and cracked insulator. Compare colour with a neighbouring plug.
- Coil swap test: move the cylinder 5 coil to cylinder 6 (or any neighbour), clear codes and drive. If P0306 appears, replace the coil. Measure coil primary resistance 0.4-2 ohm and secondary 6-15 kohm where accessible.
- Injector check: measure resistance (11-16 ohm high-impedance) and swap with a neighbour the same way. Listen for clicking with a stethoscope. A code following the injector means replace it.
- Check for vacuum leaks around cylinder 5 with a smoke machine or carefully with propane at idle while watching short-term fuel trim.
- Compression test cylinder 5: healthy petrol engines show 11-15 bar with less than 10 percent variation between cylinders. Low reading: add a spoonful of oil and retest; a rise points to rings, no rise points to valves or head gasket. Follow with a leak-down test if needed.
Frequently asked questions
Which cylinder is number 5?
It depends on the engine. On most V6 engines cylinder 5 is on the bank opposite cylinder 1; on an inline-six it is the second from the gearbox. Check the manufacturer's numbering before swapping parts.
Flashing check engine light - can I keep driving?
No. A flashing light means catalyst-damaging misfire. Stop as soon as safely possible; a new catalytic converter costs far more than a coil.
I replaced the plug and coil but P0305 is still there.
Then move on to the injector, vacuum leaks and compression. A persistent misfire on one cylinder after ignition parts are replaced is often a mechanical issue.