P0304: Cylinder 4 Misfire Detected
Can you still drive? Not recommended if the check engine light is flashing. Persistent misfires can damage the catalytic converter, leading to much more expensive repairs.
What Does P0304 Mean?
Code P0304 indicates that the engine control module has detected a misfire in cylinder 4. As with other cylinder-specific misfire codes, the problem is isolated to one cylinder, making diagnosis more straightforward. The cause is typically an ignition, fuel, or mechanical fault specific to cylinder 4.
Need to read your codes?
An OBD-II scanner lets you read and clear diagnostic trouble codes from your vehicle's computer. Most scanners work with any car made after 1996.
Browse OBD-II Scanners on AmazonCommon Causes
- Worn spark plug in cylinder 4
- Failed ignition coil
- Faulty fuel injector
- Low compression from worn piston rings
- Intake manifold gasket leak at cylinder 4
Symptoms
- Check engine light on or flashing
- Rough idle
- Reduced engine power
- Increased fuel consumption
- Possible backfiring
Diagnostic Steps
- 1Swap ignition coil and spark plug with another cylinder
- 2Test fuel injector with noid light or scan tool
- 3Perform compression test on cylinder 4
- 4Check for vacuum leaks near cylinder 4
- 5Inspect wiring harness to coil and injector
- 6Check valve adjustment if applicable
Recommended Parts & Tools
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $50 - $1200 |
| Parts Only (DIY) | $50 - $200 |
| Labor (1-3 hrs @ $100/hr) | $100 - $300 |
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Chat with AI About P0304Commonly Affected Vehicles
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Frequently Asked Questions
What is the most common cause of P0304?
The most common cause is a worn spark plug or failed ignition coil. These are inexpensive to replace and should be checked first.
Should I replace all spark plugs if only cylinder 4 is misfiring?
It is recommended to replace all spark plugs at once if they are near their service interval. If the plugs are relatively new, replacing just the one in cylinder 4 is acceptable.
Community Fix Reports
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