P0304 Error Code
📋 What Does P0304 Mean?
Cylinder 4 Misfire Detected — cylinder 4 is not firing consistently.
🔍 Common Causes
- 1Ignition coil failed on cylinder 4
- 2Spark plug worn or fouled on cylinder 4
- 3Fuel injector not firing on cylinder 4
- 4Low compression in cylinder 4
📞 When to Call a Pro
Compression test needed if coil and plug replacement does not fix the misfire.
🔧 DIY Fix Steps
- 1Swap the coil from cylinder 4 to another position and rescan — if code moves, coil is confirmed bad
- 2Inspect and replace spark plug on cylinder 4
- 3Check for oil in plug well indicating valve cover gasket leak
- 4Do not drive aggressively — catalytic converter damage risk
Frequently Asked Questions
What does P0304 mean on a Toyota vehicle?
Cylinder 4 Misfire Detected — cylinder 4 is not firing consistently.
Can I fix P0304 myself?
Yes, in many cases. Start with: swap the coil from cylinder 4 to another position and rescan — if code moves, coil is confirmed bad If that does not resolve it, compression test needed if coil and plug replacement does not fix the misfire.
How much does it cost to repair error P0304?
Estimated repair cost: $50–$500. This varies by region and technician.
Tools That Help With This Diagnosis
Basic troubleshooting tools grouped separately from the actual error-code explanation.
Multimeters
Useful for basic electrical checks when the repair path calls for it and the unit is safely isolated.
Driver sets
Useful when the first obstacle is simply reaching the part or hose involved.
Cleanup tools
Useful for drain and leak faults where standing water hides the problem.
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