This is wordy but here goes:
P0307 code definition
Cylinder 7 Misfire Detected
What the P0307 code means
When the P0307 diagnostic trouble code is stored by the Powertrain Control Module (PCM), it is an indication that a misfire has been detected in cylinder 7. More specifically, the PCM detects an increase or decrease in crankshaft revolutions per minute (RPM) that exceeds 2%.
A quick background into this system:
Each cylinder is connected to the crankshaft. On top of each cylinder is a spark plug, which uses a flammable fuel/air mixture that has been compressed inside the cylinder to fire a spark and set fire to the fuel. The fuel then releases energy to power the crankshaft. If the cylinders are not firing properly, there will be an increase or decrease in the crankshaft RPM.
What causes the P0307 code?
- Faulty spark plug in cylinder 7
- No compression in cylinder 7
- Damaged or worn out spark plug wires
- Damaged or worn spark plug coils
- Damaged distributor cap (does not apply to all vehicles)
- Damaged rotor button (does not apply to all vehicles)
- Faulty fuel injector
- Clogged exhaust gas recirculation (EGR) valves or tubes
- Burned valves
- Inaccurate ignition timing
- Vacuum leaks
- Low fuel pressure
- Head gasket leaks
- Cracked distributor cap
- Faulty camshaft sensor
- Faulty crankshaft sensor
- Faulty mass air flow (MAF) sensor
- Faulty oxygen (O2) sensor
- Faulty throttle position sensor
- Faulty catalytic converter
- Faulty PCM
What are the symptoms of the P0307 code?
- Check Engine Light that is on or flashing (dependant on severity of misfire condition)*
- Vehicle that is difficult to start or will not start at all
- Vehicles stalls during acceleration
- Vehicle randomly stalls or dies at stops
- Vehicle engine runs rough
- Vehicle idles rough
- Vehicle lacks power while driving
- Increase of fuel consumption
- Vehicle has no symptoms (rare)
*If the increase or decrease in crankshaft RPM is between 2-10%, the Check Engine Light will illuminate and remain steady. However, if the crankshaft RPM exceeds 10%, the Check Engine Light will illuminate and blink continuously. A variation of more than 10% in crankshaft RPM indicates a serious misfiring condition.
How does a mechanic diagnose the P0307 code?
- Uses an OBD-II scanner to get all of the trouble codes and freeze frame data that has been stored by the PCM
- Clears codes, then performs a test drive to see if code P0307 returns
- Inspects the spark plug wire for cylinder 7 for wiring that is damaged or worn out
- Inspects the spark plug for cylinder 7 for damaged or excessive wear
- Inspects coil packs and coil pack wiring for corrosion, breaks, excessive wear, or other damage
- Inspects the distributor cap and rotor button for corrosion, cracks, excessive wear, or other damage (if vehicle has distributor cap and rotor button system)
- Replaces or repairs damaged spark plugs, coil packs, spark plug wiring, and/or coil pack wiring
- Inspects the fuel injectors and fuel injector wiring if the P0307 code returns after any damaged spark plugs, coil packs, spark plug wires, and/or coil pack wiring has been replaced
- Diagnoses and repairs any other trouble codes and performs another test drive to see if the P0307 code returns
- If the P0307 code returns, inspects the compression system for cylinder 7
If clearing the P0307 diagnostic trouble code fails, the PCM may need to be replaced or reprogrammed. This is not common, but should be considered as a possibility when other diagnostic measures have not resolved the misfire condition.
Common mistakes when diagnosing the P0307 code
A common mistake is neglecting to rule out all of the possible causes for the misfire condition.
Visually inspect the fuel injector wiring before replacing spark plugs, spark plug wiring, coil packs, and coil pack wiring. In addition to ruling out the a faulty cylinder, other related stored trouble codes will need to be diagnosed and repaired. Taking time to address the other possible causes of the misfiring condition during the diagnostic process may save a lot of time.
How serious is the P0307 code?
A vehicle with a misfiring condition could shut down completely, or not start at all. These driveability issues make operation of a vehicle unreliable and hazardous. For this reason, the P0307 diagnostic trouble code is one that is considered serious. This condition should be addressed and repaired as soon as possible.
What repairs can fix the P0307 code?
Additional comments for consideration regarding the P0307 code
If one of the spark plugs is damaged and needs to be replaced, it will be necessary to replace all of the spark plugs. A good way to determine if a defective wire or coil pack is causing the misfire is to switch the wire and/or coil pack with another wire and/or coil pack. If a new trouble code comes back for a different cylinder, it is an indication that the misfiring condition is being caused by the wire and/or coil pack. It may also be possible that the vehicle is in need of a tune-up.
It is also necessary to gap the spark plugs properly, as not doing so can cause a misfiring condition. To gap the spark plugs correctly, a feeler gauge will be required. Manufacturer specifications should be used when gapping the spark plugs. These specifications can be found on a sticker, under the hood of the vehicle.
