P0304 - Cylinder 4 Misfire Detected
P0304 is a generic powertrain diagnostic trouble code indicating Cylinder 4 Misfire Detected. It relates to the Ignition System / Misfire system.
DTC Breakdown (SAE J2012)
| System | Powertrain (P) |
| Type | Generic |
| Subsystem | Ignition System / Misfire |
| Fault Index | 04 |
| Standard | SAE J2012 / ISO 15031-6 |
What does diagnostic code P0304 mean?
The engine control unit has detected that cylinder number 4 is misfiring and failing to contribute to engine power output.
Severity Level & Driveability Details
Severity: High
Raw fuel will enter the catalytic converter, causing overheating and melting. A flashing check engine light indicates active misfires in Cylinder 4.
Common Symptoms of P0304
- Continuous flashing MIL warning light indicating catalyst danger.
- Rough running engine with heavy shaking at idle.
- Loss of power under acceleration.
- Gasoline odor from exhaust.
Typical Causes for P0304
- Burnt or fouled spark plug in cylinder 4.
- Failed cylinder 4 ignition coil.
- Faulty fuel injector in cylinder 4.
- Cylinder 4 compression loss (burnt valve, blown head gasket).
Diagnostic and Troubleshooting Steps
Swap the cylinder 4 ignition coil with cylinder 3. If the misfire shifts to cylinder 3 (P0303), replace the coil. If the misfire persists, inspect the spark plug, injector, and perform a compression test.
Typical Repairs and Fixes
- Replacing the ignition coil or spark plug in cylinder 4.
- Replacing the cylinder 4 fuel injector.
- Performing a valve job or replacing head gasket if compression is low.
Sensor Location & Parts Involved
The ignition coil and spark plug for cylinder 4 are located on top of the cylinder head on the engine block.
Clearing Code & Recurrence
Resolve the underlying ignition or fuel fault in cylinder 4, then reset the codes using an OBD2 scanner.
Emissions & Smog Inspection Impact
Misfiring in cylinder 4 releases unburned hydrocarbons into the exhaust stream, potentially damaging the catalytic converter and raising emissions.
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Related Diagnostic Codes
Sources & References
This diagnostic guide is compiled and verified against the following authority sources:
- NHTSA Recall Database
- EPA OBD II Regulations
Frequently Asked Questions about P0304
What does the cylinder 4 misfire code P0304 mean?
The engine control module logged P0304 after detecting a combustion misfire in cylinder 4. This indicates that the fuel-air mixture is failing to ignite properly inside the cylinder 4 chamber.
Is it safe to drive with the cylinder 4 misfire code P0304 active?
No, driving with active misfires in cylinder 4 can ruin the catalytic converter.
How much does it cost to repair a cylinder 4 misfire code P0304 fault?
Replacing an ignition coil or spark plug for cylinder 4 typically costs $100-$300. Replacing the fuel injector for cylinder 4 costs $200-$450.
What are the common causes of the cylinder 4 misfire code P0304?
Trigger conditions for the cylinder 4 misfire code P0304 include: A worn or fouled spark plug in cylinder 4., Failed ignition coil or damaged spark plug wire for cylinder 4., Faulty fuel injector or poor fuel atomization in cylinder 4..
Can I clear the check engine light for cylinder 4 misfire code P0304?
Resolve the underlying ignition or fuel fault in cylinder 4, then reset the codes using an OBD2 scanner.
Will the cylinder 4 misfire code P0304 cause an inspection failure?
Misfiring in cylinder 4 releases unburned hydrocarbons into the exhaust stream, potentially damaging the catalytic converter and raising emissions.