The vehicle engine contains multiple cylinders in which the air-fuel mixture combusts. The combustion of the air-fuel mixture produces the power that is used to run the vehicle. The proper combustion of the mixture is very important for the efficient performance of the engine. The cylinder misfires whenever the air-fuel mixture doesn’t properly burn in any of your engine cylinders. When a vehicle computer detects a misfire, it triggers a specific code. Whenever cylinder number 6 suffers a misfire, a trouble code P0306 is stored. This article mainly explains the P0306 code causes, symptoms, and how to fix it.
P0306 Code Definition
The P0306 code stands for “Cylinder 6 Misfire Detected.”
What Does the P0306 Code Mean?
The P0306 code indicates that your powertrain control module (PCM) has detected a misfire on cylinder number 6.
The vehicles usually contain 4, 6, or 8 cylinders. These cylinders are arranged in different arrangements.
To increase the engine power, you will need to increase the number of cylinders. A piston moves upward and downward inside the cylinder at a specific time.
Misfires are produced due to insufficient combustion or lack of combustion of the air-fuel mixture inside the engine cylinder. The combustion takes place when the pressurized fuel-air mixture ignites in the cylinder above each piston.
Precise combustion timing is very important for optimal performance and efficiency. Due to the combustion of the air-fuel mixture, power is generated, which is used to run the vehicle.
When your engine cylinder misfires, the crankshaft speed is reduced because the cylinder did not have a combustion event or burned more than a set number of times during the 200 or 1000 rpm window, and the PCM monitors it and triggers a misfire code.
When your powertrain control module (PCM) detects a misfire on engine cylinder number 6, it triggers the trouble code P0306.
Causes of P0306 Code
One or more of the following causes triggers the P0306 code:
- Bad compression system
- Faulty or worn spark plugs
- Damaged spark plug wiring
- Faulty fuel pressure sensor
- Damaged or bad O2 sensor
- Ignition problems, including failing or damaged ignition coils
- Bad MAF sensor
- Insufficient or contaminated fuel
- Burned or bad engine valves
- Ignition spark leaking from spark plug wire or plug boot
- Clogged or bad EGR valve
- Bad ignition coils in cylinder 6
- Bad fuel injectors
- Bad fuel pump
- Damaged distributor cap
- Head gasket leaks
- Faulty oil distributor
- A damaged lifter or worn camshaft lobe
- Low fuel pressure
- A faulty crankshaft position sensor
- A bad throttle position sensor
- Vacuum leaks
- A faulty camshaft position sensor
- Bad PCM
Symptoms of P0306 Code
A vehicle with the P0306 code may produce one or more of the following symptoms:
- Illuminated check engine light
- Engine stalling
- Rough idle
- Fuel smell from the exhaust pipe
- The vehicle will not start or is difficult to start
- Limp mode
- Poor fuel economy
- Poor car acceleration
- Misfires
- A reduction in the engine power
- The engine runs rough, hesitates, or jerks when accelerating
How to Diagnose the P0306 Trouble Code?
Follow the below-given steps to diagnose the P0306 code:
- Use an OBD2 scan tool to ensure the existence of the P0306 trouble codes. Utilize the freeze frame data to check what’s going on. Continue the troubleshooting based on the other trouble codes you may find.
- Clear the codes and take your vehicle for a test drive. If the codes return, then check other parts.
- Inspect for loose connections
- Inspect the wires for damage (especially cylinder 6).
- Inspect the loose engine ground wiring.
- Visually inspect the spark plugs and spark plug wiring. If your car has an individual coil pack other than the spark plug wires, first remove the coil from cylinder #6 and replace it with the coil of cylinder #2. Now check; if your engine misfiring is due to cylinder #2 (P0302), it means the coil pack is defective, and you should replace it. The same test can be done for the spark plugs of cylinder #6, i.e., moving spark plugs from cylinder #6 to cylinder #1, and if the trouble code is P0301, it means your spark plug is bad. If necessary, replace the spark plug and spark plug wiring and again check for the misfire.
- If your ignition system is working efficiently, there may be an issue within the fuel system. For this, inspect the components of the fuel system, such as the fuel injector, fuel pump, fuel regulator, and fuel pressure sensor. You must also check the fuel level and fuel pressure. Low fuel pressure may lead to irregular misfires on multiple cylinders.
- After the fuel system and ignition system inspection, perform a compression test and leak-down test to check if any engine mechanical issues are causing the misfire. The mechanical parts (such as worn valve guides, head gasket leak, damaged valve, bad piston ring, or damaged valve spring) may cause the engine to misfire.
- Check the intake system for vacuum leaks. If there is any leak, repair it properly.
- If your vehicle contains a distributor cap and ignition cables, inspect them and replace them if needed.
- Inspect the shaft or timing belt and replace them if needed.
- If all the above parts are working efficiently, and you are still getting the P0306 code, your PCM may be bad.
Common P0306 Diagnosis Mistakes
- Not properly inspecting all the parts
- Replacing the unnecessary components
- Inability to confirm the presence of the P0306 code.
- Not clearing the PCM codes after fixing the codes.
- Not shifting the coil of cylinder 6 to a different cylinder to check if the misfire moves to another cylinder. This would show a bad coil.
- Not substituting one part at a time with a different cylinder to isolate the faulty part.
What repairs can fix the P0306 Code?
One or more of the following repairs can fix the P0306 engine code:
- Replacing the faulty spark plug
- Replacing the bad compression system
- Replacing the bad distributor
- Replacing the faulty fuel pump
- Replacing or repairing the damaged cylinder
- Fixing the vacuum leaks
- Replacing or fixing the head gasket leaks in cylinder 6
- Replacing or repairing the damaged coil pack
- Replacing the damaged spark plug wiring
- Replacing the bad or damaged fuel injectors of cylinder 6
- Replacing the faulty camshaft position sensor
- Replacing the faulty O2 sensor at cylinder 6
- Replacing the faulty crankshaft position sensor
- Diagnosing and repairing any other misfire-related trouble codes stored by the PCM
Repair Cost of P0306 Code
After diagnosing, the P0306 code may need one of the following repairs to fix the original problem.
| Parts | Cost |
| Spark Plug replacement | $60 to $260 |
| Fuel pump replacement | $250 to $1,090 |
| Fuel injector replacement | $1400 to $2000 |
| Ignition Coils | $220 to $650 |
| Spark plug wiring repair | $170 to $250 |
FAQ Section
Can I drive with a cylinder 6 misfire?
No, you shouldn’t drive with an engine misfire. Driving with a misfire is very dangerous and can damage your engine.
How serious is the P0306 Code?
The diagnostic trouble code P0306 is considered a serious problem. This code indicates the engine misfired. Driving with an engine misfire is very hazardous, especially if your vehicle starts to stall in the middle of the road.
Therefore, you must fix the P0306 trouble code immediately. The engine misfire may also badly damage the parts of the engine.
How much is it to fix a cylinder 6 misfire?
If your cylinder number 6 misfires, it will likely cost between $190 and $620 to fix the problem. The exact cost will depend on the cause of the misfire and the make and model of your vehicle. If you need to replace the spark plugs or ignition coils, the lower end of the spectrum will be the cost.
Can a misfire ruin an engine?
If left untreated, a cylinder misfire can lead to significant engine damage. Worse, if you experience a bad misfire while driving, it could result in an accident. This is why it’s important to treat engine misfires as soon as you detect them.
Can a bad O2 sensor cause a random misfire code?
Yes. The O2 sensor is a major part of the fuel injection system. Your vehicle powertrain control module (PCM) uses this input of this sensor to fuel control. The failure of the O2 sensor may result in an incorrect air-fuel ratio. In addition, it can lead to engine misfiring and set code P0300.