P0308 - Cylinder 8 Misfire Detected
P0308 indicates the PCM detected a combustion misfire. Treat the code as a starting point for testing spark, fuel, air, and mechanical condition before replacing parts.
Code first. Confirm symptoms and checks before pricing parts.
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Common Next Steps
Turn the code into the next check.
Check coil boots, carbon tracking, and whether the miss follows a swap.
Inspect gap, fouling, wear, oil, coolant, and plug-well condition.
Move to injector balance, pulse, or leak-down checks if the misfire stays.
Use compression or leak-down testing when spark and fuel checks do not move the fault.
Related Inspection
Code Overview
P0308 indicates the PCM detected a combustion misfire. Treat the code as a starting point for testing spark, fuel, air, and mechanical condition before replacing parts.
Common Causes
- Worn, fouled, cracked, or incorrectly gapped spark plug
- Ignition coil or coil boot breaking down under heat or load
- Injector restricted, leaking, unplugged, or not being commanded correctly
- Vacuum leak, intake runner leak, PCV leak, or unmetered air affecting one or more cylinders
- Low compression, valve sealing issue, timing issue, or head gasket seep
- Fuel pressure or volume problem on random or multiple-cylinder misfires
Symptoms
- Rough idle, shaking, or engine vibration
- Flashing or steady check engine light
- Hesitation or bucking under load
- Fuel smell, poor fuel economy, or catalyst overheating risk
Diagnostic Steps
- Record freeze-frame data and identify whether the misfire is cold-start, idle, cruise, or load related
- Check live misfire counters and note whether the fault stays on one cylinder or moves between cylinders
- Inspect plugs, coil boots, connectors, harness routing, oil intrusion, coolant evidence, and carbon tracking
- Swap coil or plug only when the test can prove whether the misfire follows the part
- Verify injector pulse, injector balance, and fuel pressure or volume when ignition checks pass
- Perform compression, leak-down, relative compression, or cooling-system pressure checks before condemning mechanical parts
Repair Difficulty
Moderate
General difficulty estimate for the most common repair path.
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Next Steps
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