P0306 – Cylinder 6 Misfire Detected means the engine control module (ECM/PCM) has identified that cylinder 6 is not firing correctly. This can be caused by ignition faults, fuel delivery issues, compression problems, or wiring failures. A misfire in one cylinder leads to rough running, hesitation, power loss, and increased emissions. If ignored, it can damage the catalytic converter. This guide explains what P0306 means, the symptoms, causes, detailed diagnosis steps, and the best repair options.
What Does P0306 Mean?
P0306 is a generic OBD-II powertrain code set when the ECM detects a misfire on cylinder 6 based on crankshaft speed variation. When one cylinder fails to contribute power, the crankshaft slows momentarily, and the ECM logs the event as a misfire.
This code doesn’t specify the root cause—it only identifies the affected cylinder. Ignition, fuel, air, mechanical, or sensor issues can all trigger P0306. Because misfires can quickly overheat the catalytic converter, prompt diagnosis is crucial.
Quick Reference
- OBD-II Family: P-Code (Powertrain)
- Scope: Generic
- System: Ignition / Fuel / Engine Mechanical
- Difficulty Level: Moderate
- Estimated Repair Cost: €50–€550+
- Last Updated: 28 November 2025
Real-World Example / Field Notes
A V6 pickup arrived with rough idle and poor acceleration. Live data confirmed misfires on cylinder 6. Swapping the coil with cylinder 4 caused the misfire to move—confirming the ignition coil was defective. Replacing the coil and the spark plug fixed the issue immediately.
Another case involved a sedan with an intermittent P0306 only when the engine was hot. A leaking injector dripped fuel into cylinder 6 after shutdown, causing a misfire on restart. Installing a new injector and performing a fuel-trim relearn resolved the problem.
Symptoms of P0306 – Cylinder 6 Misfire Detected
- Rough idle: Engine shakes or vibrates noticeably.
- Loss of power: Weak acceleration or hesitation under load.
- Engine shaking: More noticeable at low RPM.
- Check engine light flashing: Indicates severe, catalyst-damaging misfire.
- Poor fuel economy: Misfires waste fuel and affect combustion.
- Fuel smell: Unburned fuel entering exhaust.
- Hard starting: Especially if cylinder 6 has fuel or compression issues.
Common Causes of P0306
Most Common Causes
- Faulty ignition coil for cylinder 6
- Worn or fouled spark plug
- Leaking or clogged fuel injector
- Vacuum leak near cylinder 6 intake runner
- Low compression due to valve or piston issues
Less Common Causes
- Faulty crankshaft or camshaft position sensor
- Wiring damage to coil or injector harness
- PCM/ECM driver failure
- Fuel pressure problems from weak pump or clogged filter
- Carbon buildup on intake valves (direct-injection engines)
Diagnosis: Step-by-Step Guide
P0306 diagnosis focuses on isolating whether the misfire is due to ignition, fuel, or mechanical problems.
Tools You’ll Need
OBD-II scanner, spark plug socket, multimeter, fuel pressure gauge, compression tester, noid light or injector tester, and basic hand tools.
- Check for additional codes: Look for P0300, fuel-trim codes, or sensor faults.
- Inspect spark plug: Remove cylinder 6 spark plug and check for fouling, cracks, or wear.
- Swap ignition coil: Move the coil from cylinder 6 to another cylinder; see if misfire follows.
- Check injector function: Use a stethoscope or scan tool to confirm clicking; perform balance test if available.
- Check injector wiring: Back-probe connector for proper voltage and ground.
- Look for vacuum leaks: Inspect intake gasket and hoses near cylinder 6.
- Perform compression test: Compare cylinder 6 to other cylinders.
- Test fuel pressure: Verify system meets factory specs under load.
- Review Mode $06: Look at misfire counters and cylinder contribution data.
- Check mechanical timing: If multiple cylinders misfire, verify timing chain/belt alignment.
Pro Tip: If the misfire only happens on cold start or after rain, inspect coil boots and spark plug wells for moisture intrusion.
Possible Fixes & Repair Costs
- Replace ignition coil: €40–€120
- Replace spark plug: €10–€30
- Replace or clean fuel injector: €60–€180
- Repair wiring to coil or injector: €30–€120
- Fix vacuum leaks (gaskets/hoses): €20–€80
- Engine repair (valve/piston/compression): €250–€1,000+ depending on severity
Can I Still Drive With P0306?
Driving with P0306 is not recommended. A misfire sends unburned fuel into the catalytic converter, causing overheating and permanent damage. The vehicle may also hesitate or stall under load, creating unsafe driving conditions. Repair the issue as soon as possible.
Related Codes
- P0399 – Ignition Coil “R” Primary/Secondary Circuit
- P0364 – Reserved
- P0363 – Misfire Detected Fueling Disabled
- P0362 – Ignition Coil “L” Primary/Secondary Circuit
- P0361 – Ignition Coil “K” Primary/Secondary Circuit
- P0360 – Ignition Coil “J” Primary/Secondary Circuit
- P0359 – Ignition Coil “I” Primary/Secondary Circuit
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0357 – Ignition Coil “G” Primary/Secondary Circuit
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
Key Takeaways
- P0306 means cylinder 6 is misfiring due to ignition, fuel, or mechanical issues.
- Coils, spark plugs, and injectors are the most common causes.
- Driving with a misfire can damage the catalytic converter.
- Systematic testing helps pinpoint the root cause quickly.
FAQ
Is P0306 always caused by the ignition coil?
No. While coils commonly fail, injectors, vacuum leaks, or compression problems can also trigger P0306.
Can a dirty injector cause P0306?
Yes. Injectors that clog or stick can starve cylinder 6 of fuel, leading to misfires.
What if the misfire only happens under load?
This usually indicates an ignition coil breaking down or weak fuel delivery at higher demand.
Can a bad O2 sensor cause a cylinder-specific misfire?
Not directly. O2 sensors affect fuel trims globally, but misfires are cylinder-specific faults.
How quickly should I fix P0306?
Immediately. A flashing check engine light means misfire levels are high enough to damage the catalytic converter.