P0307 Code: Causes, Symptoms, Diagnosis & How to Fix It
The P0307 code means Cylinder 7 Misfire Detected.
This generic OBD2 trouble code is triggered when the engine computer detects that cylinder 7 is not firing properly. P0307 identifies the affected cylinder, but it does not identify the failed component.
The problem can involve the ignition system, fuel delivery, air intake, engine compression, wiring, or engine timing. The exact location of cylinder 7 depends on the engine design, so use the vehicle manufacturer's service information before testing parts.
P0307 Code Symptoms
Common symptoms include:
Check Engine Light
Rough or shaking engine
Rough idle
Hesitation or stumbling
Reduced engine power
Poor fuel economy
Hard starting
Engine stalling
Unusual exhaust smell
Flashing Check Engine Light
A severe misfire can make the engine jerk or run very unevenly, especially during acceleration. A flashing Check Engine Light can indicate a misfire severe enough to risk catalytic-converter damage.
Common Causes of P0307
1. Worn or Faulty Spark Plug
A fouled, damaged, worn, or incorrectly gapped spark plug may prevent cylinder 7 from producing consistent combustion.
2. Bad Ignition Coil
A weak or failed ignition coil can cause cylinder 7 to lose its spark. On vehicles with individual coils, a coil-swap test can help determine whether the misfire follows the coil.
3. Faulty Fuel Injector
A clogged, restricted, leaking, or electrically defective injector may deliver the wrong amount of fuel to cylinder 7.
4. Vacuum or Intake Leak
Unmetered air entering the intake can create an incorrect air-fuel mixture and contribute to a misfire.
5. Low Fuel Pressure
A weak fuel pump or another fuel-delivery problem can cause inadequate fuel supply and misfires, particularly under load.
6. Low Engine Compression
A burned valve, worn piston rings, damaged piston, or head-gasket problem can reduce compression and cause a persistent misfire.
7. Wiring or Connector Faults
Damaged wiring, corrosion, loose connectors, or poor electrical connections can interfere with the ignition or fuel system.
8. Engine Timing Problems
Incorrect valve or ignition timing can prevent cylinder 7 from completing combustion correctly.
How to Diagnose P0307
1. Scan for Additional Codes
Connect an OBD2 scanner and check for stored and pending codes. Record the freeze-frame information before clearing the codes.
Look for additional misfire, fuel, lean-condition, sensor, or ignition codes.
2. Inspect the Spark Plug
Remove the cylinder 7 spark plug and check for:
Carbon buildup
Oil or fuel fouling
Worn electrodes
Incorrect gap
Cracks or physical damage
Spark-plug condition can provide useful clues about the source of the misfire.
3. Test the Ignition Coil
Inspect the coil, boot, connector, and wiring.
If the vehicle uses interchangeable ignition coils, move the suspected coil to another cylinder. If the misfire moves with the coil, the coil is a strong suspect.
4. Check the Fuel Injector
Inspect the cylinder 7 injector and connector. Depending on the vehicle, testing may include electrical checks, injector resistance, fuel delivery, or injector-balance testing.
5. Check for Vacuum Leaks
Inspect vacuum hoses and intake components around the affected cylinder. A smoke test can help locate leaks that are difficult to see visually.
6. Perform a Compression Test
If the ignition and fuel systems appear normal, test engine compression.
Low compression can indicate an internal mechanical problem involving a valve, piston, piston rings, or head gasket.
7. Check Timing and Sensor Data
If basic ignition, fuel, and compression checks do not identify the problem, inspect camshaft/crankshaft synchronization and relevant engine-management data according to the manufacturer's procedure.
How to Fix P0307
The correct repair depends on the confirmed cause. Possible repairs include:
Replace the faulty spark plug
Replace a defective ignition coil
Repair ignition wiring or connectors
Replace or repair the fuel injector
Repair an intake or vacuum leak
Correct fuel-pressure problems
Repair engine timing issues
Repair an internal mechanical problem
Replace a failed sensor when testing confirms it
After the repair, clear the code and perform a test drive while monitoring misfire data.
P0307 does not automatically mean the ignition coil is bad. The code identifies the cylinder experiencing the misfire, not the component that caused it.
Is P0307 Serious?
P0307 should be diagnosed promptly. A continuing misfire can reduce performance and fuel economy and may damage the catalytic converter.
If the Check Engine Light is flashing, the engine is shaking severely, the vehicle has major power loss, or it is stalling, avoid unnecessary driving and have it inspected promptly.
If the Check Engine Light is steady and symptoms are mild, arrange diagnosis as soon as practical.
P0307 vs. P0306
Code | Meaning |
P0306 | Cylinder 6 Misfire Detected |
P0307 | Cylinder 7 Misfire Detected |
Both codes indicate cylinder-specific misfires. The difference is the cylinder identified by the engine computer.
P0307 vs. P0300
P0300 indicates a random or multiple-cylinder misfire without identifying one specific cylinder.
P0307 specifically identifies cylinder 7 as the affected cylinder.
Frequently Asked Questions
Can a bad spark plug cause P0307?
Yes. A worn, fouled, damaged, or incorrectly gapped spark plug can cause cylinder 7 to misfire.
Can a bad ignition coil cause P0307?
Yes. A defective ignition coil can prevent cylinder 7 from receiving a reliable spark.
Can I drive with P0307?
Avoid driving if the Check Engine Light is flashing, the engine is shaking severely, or there is major power loss or stalling. A severe misfire can damage the catalytic converter.
Does P0307 mean cylinder 7 itself is damaged?
No. P0307 identifies a misfire in cylinder 7. The underlying cause could be ignition, fuel, air, compression, wiring, or timing.
Can low compression cause P0307?
Yes. Low compression from a valve, piston, piston-ring, or head-gasket problem can produce a persistent cylinder 7 misfire.
