P0306
PowertrainCylinder 6 Misfire Detected
Cylinder 6 is misfiring. Like P0305, this only shows up on engines with six or more cylinders.
ⓘ Information only. This page provides general educational information about fault code P0306. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0306 mean?
P0306 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 6 Misfire Detected.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light
- • Rough idle and noticeable vibration
- • Power loss under acceleration
- • Slightly increased fuel use
- • Sometimes a 'put-put' or muffled sound from the exhaust at idle
Possible causes
Causes commonly associated with P0306, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Worn or fouled spark plug
- 2. Failed ignition coil
- 3. Faulty fuel injector
- 4. Vacuum leak around cylinder 6's intake port (split hose, leaking gasket)
- 5. On older or higher-mileage engines, low compression on that cylinder
- 6. Carbon-fouled valves on direct-injection engines
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Identify cylinder 6's position on the engine
- 2. Inspect the plug, coil, and injector visually
- 3. Coil swap test, easiest and cheapest diagnostic move
- 4. Live data on misfire counter for cylinder 6 versus the others, the gap is often telling
- 5. Compression test and, if still ambiguous, a leak-down test
Common questions about P0306
Why do direct-injection engines misfire more often? +
On port-injection engines, fuel washes over the back of the intake valves on every cycle, keeping them clean. Direct-injection engines spray fuel into the cylinder itself, so the valves never see fuel and carbon builds up over time. By 50,000-80,000 miles, it can be enough to disrupt airflow and trigger cylinder-specific misfires.
Should I get a walnut blast? +
Walnut blasting (using crushed walnut shells in a vacuum tool to clean carbon off the intake valves) is the proven workshop fix for direct-injection carbon buildup. It's £200-£400 typically. Chemical cleaners help marginally but rarely solve a confirmed carbon problem.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →