P0306
Cylinder 6 Misfire Detected
Get Your FREE AI Diagnostic Report
Enter your vehicle for a personalized diagnosis for code P0306
The P0306 trouble code indicates that your vehicle's engine control module (ECM) has detected a misfire in cylinder 6. A misfire occurs when the air-fuel mixture in a cylinder fails to ignite properly or burns incompletely during the combustion cycle. The ECM monitors engine speed and crankshaft position to detect irregularities in how smoothly each cylinder fires. When cylinder 6 consistently fails to produce the expected power output, the computer logs code P0306 and illuminates the check engine light to alert you to the problem.
This code matters because an ongoing misfire can damage your catalytic converter over time, as unburned fuel enters the exhaust system and causes it to overheat. Additionally, misfires reduce engine performance, waste fuel, and can lead to more serious engine damage if left unaddressed. You may notice rough idling, hesitation during acceleration, or a noticeable decrease in power. The longer a misfire continues, the higher the risk of damaging expensive emission control components.
When you encounter code P0306, you should address it within the week to prevent further damage and restore normal engine operation. Start with the simplest and most common causes: inspect and replace the spark plug in cylinder 6 if it shows wear, and check the ignition coil for that cylinder. Many DIY mechanics can handle these basic repairs with common tools. If the problem persists after addressing these components, further diagnosis may be needed to check fuel injectors, compression levels, or vacuum leaks. Professional mechanics can perform more advanced diagnostic tests to pinpoint the exact cause and prevent unnecessary part replacement.
Severity
Symptoms
- •Check Engine Light illuminated
- •Noticeable engine shaking or rough idle
- •Reduced engine power and acceleration
- •Poor fuel economy
- •Engine stumbling or hesitation during acceleration
- •Strong smell of unburned fuel from exhaust
Likely Causes
Spark plugs wear over time and can fail to ignite the air-fuel mixture properly. Carbon buildup, electrode wear, or incorrect gap are common issues that prevent proper combustion in the affected cylinder.
The ignition coil generates the high voltage needed to create a spark. When it fails, cylinder 6 cannot fire properly, resulting in a misfire that the engine computer detects.
A dirty or malfunctioning fuel injector may not deliver the correct amount of fuel to cylinder 6, creating an improper air-fuel mixture that causes misfires and poor combustion.
Internal engine wear, burned valves, or damaged piston rings can reduce compression in cylinder 6, preventing proper combustion even when spark and fuel delivery are adequate.
Air leaks in the intake system can create a lean condition specifically affecting cylinder 6, disrupting the proper air-fuel ratio and causing intermittent or constant misfires.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace spark plug for cylinder 6
- Replace ignition coil or coil pack for cylinder 6
- Clean or replace fuel injector for cylinder 6
- Swap ignition coil with another cylinder to confirm diagnosis
- Perform compression test and repair valves or piston rings if low compression found
Shop Parts
Videos
P0300 Explained - Random/Multiple Cylinder Misfire Detected (Simple Fix)
FIXD
How to Fix a Random Engine Misfire in Your Car (Code P0300)
Scotty Kilmer
Spark Plug Replacement DIY (the ULTIMATE Guide)
ChrisFix