P0303 - Cylinder 3 Misfire Detected
P0303 is a generic powertrain diagnostic trouble code indicating Cylinder 3 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 | 03 |
| Standard | SAE J2012 / ISO 15031-6 |
What does diagnostic code P0303 mean?
The engine computer has detected a misfire condition specifically localized to cylinder number 3.
Severity Level & Driveability Details
Severity: High
Misfiring dumps raw gasoline into the catalytic converter, causing it to overheat and melt. Stop driving if the light flashes.
Common Symptoms of P0303
- Shaking engine at idle.
- Poor throttle response and power loss.
- Continuous flashing check engine light signifying active misfires.
- Unburned fuel smell.
Typical Causes for P0303
- Faulty ignition coil for cylinder 3.
- Worn or fouled spark plug in cylinder 3.
- Bad cylinder 3 fuel injector.
- Low cylinder 3 compression due to valve or ring wear.
Diagnostic and Troubleshooting Steps
Swap the cylinder 3 coil with cylinder 4. If the misfire moves to cylinder 4 (P0304), the coil is bad. Otherwise, check the plug, injector, and cylinder compression.
Typical Repairs and Fixes
- Replacing cylinder 3 spark plug or ignition coil.
- Replacing the cylinder 3 fuel injector.
- Repairing engine compression issues.
Sensor Location & Parts Involved
The ignition coil and spark plug for cylinder 3 are located on top of the cylinder head on the engine block.
Clearing Code & Recurrence
Resolve the underlying ignition or fuel fault in cylinder 3, then reset the codes using an OBD2 scanner.
Emissions & Smog Inspection Impact
Misfiring in cylinder 3 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 P0303
What does the cylinder 3 misfire code P0303 mean?
The engine control module logged P0303 after detecting a combustion misfire in cylinder 3. This indicates that the fuel-air mixture is failing to ignite properly inside the cylinder 3 chamber.
Is it safe to drive with the cylinder 3 misfire code P0303 active?
No, driving with active misfires in cylinder 3 can ruin the catalytic converter.
How much does it cost to repair a cylinder 3 misfire code P0303 fault?
Replacing an ignition coil or spark plug for cylinder 3 typically costs $100-$300. Replacing the fuel injector for cylinder 3 costs $200-$450.
What are the common causes of the cylinder 3 misfire code P0303?
Trigger conditions for the cylinder 3 misfire code P0303 include: A worn or fouled spark plug in cylinder 3., Failed ignition coil or damaged spark plug wire for cylinder 3., Faulty fuel injector or poor fuel atomization in cylinder 3..
Can I clear the check engine light for cylinder 3 misfire code P0303?
Resolve the underlying ignition or fuel fault in cylinder 3, then reset the codes using an OBD2 scanner.
Will the cylinder 3 misfire code P0303 cause an inspection failure?
Misfiring in cylinder 3 releases unburned hydrocarbons into the exhaust stream, potentially damaging the catalytic converter and raising emissions.