P0308
Cylinder 8 Misfire Detected
The engine is not burning fuel properly in cylinder 8. This can cause rough running, poor power, fuel smell, and damage to the catalytic converter if ignored.
- SEV
- 4/5
- DRIVE
- CAUTION
- DIY
- $20–$250
- SHOP
- $150–$1,000
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Faulty spark plug in cylinder 8
- Bad ignition coil or coil boot on cylinder 8
- Fuel injector for cylinder 8 clogged, weak, or not firing
Typical repair cost
DIY usually runs $20–$250. Typical shop repair lands around $150–$1,000, depending on the root cause.
01 / Definition
P0308 is set when the engine computer detects misfire events on cylinder 8. The misfire may be caused by ignition, fuel delivery, air leak, compression loss, or wiring problems affecting that specific cylinder. If the misfire is severe or persistent, unburned fuel can overheat and damage the catalytic converter.
02 / Drive status
With caution. You may be able to drive a short distance, but continued driving can damage the catalytic converter and worsen the misfire. If the engine is shaking badly, flashing the check engine light, or lacking power, stop driving and diagnose it right away.
03 / Symptoms
- Rough idle
- Engine shaking or vibration
- Loss of power
- Check engine light on or flashing
- Poor fuel economy
- Fuel smell from exhaust
- Hard starting or hesitation
- Misfire felt under acceleration
04 / Causes
| 1 | Faulty spark plug in cylinder 8 | high |
|---|---|---|
| 2 | Bad ignition coil or coil boot on cylinder 8 | high |
| 3 | Fuel injector for cylinder 8 clogged, weak, or not firing | medium |
| 4 | Vacuum leak or intake manifold leak near cylinder 8 | medium |
| 5 | Worn engine compression issue such as bad valve, piston ring, or head gasket leak | medium |
| 6 | Damaged wiring, connector, or PCM control issue for cylinder 8 ignition/injector circuit | low |
| 7 | Incorrect fuel pressure or contaminated fuel | low |
05 / Diagnostic sequence
- 01Scan for all stored codes and freeze-frame data, and check whether P0308 appears with fuel trim or injector/coil codes.
- 02Inspect the spark plug in cylinder 8 for wear, fouling, cracking, or fuel/oil deposits.
- 03Swap the cylinder 8 ignition coil with another cylinder and see whether the misfire follows the coil.
- 04Check the cylinder 8 spark plug boot, coil connector, and wiring for corrosion, looseness, or heat damage.
- 05Test the fuel injector on cylinder 8 for pulse, resistance, and proper operation; listen for injector clicking if possible.
- 06Inspect for vacuum leaks, intake gasket leaks, or air leaks near the affected cylinder.
- 07Perform a compression test and, if needed, a leak-down test to check for mechanical engine damage.
- 08Verify fuel pressure and rule out contaminated or poor-quality fuel if multiple cylinders are affected.
06 / Repairs
| 1 | Replace worn or fouled spark plug on cylinder 8 | $20–$80 |
|---|---|---|
| 2 | Replace faulty ignition coil, coil boot, or related wiring repair | $60–$250 |
| 3 | Clean or replace clogged or failed fuel injector | $80–$350 |
| 4 | Repair vacuum leak, intake gasket leak, or damaged hose | $50–$400 |
| 5 | Repair internal engine mechanical problem such as valve, ring, or head gasket issue | $500–$2,500 |
| 6 | Repair wiring, connector, or PCM control fault after testing | $100–$800 |
07 / Related codes
08 / FAQ
Is P0308 serious?
Yes. A misfire can damage the catalytic converter and may leave you stranded if the problem gets worse.
Can I keep driving with P0308?
Short trips may be possible if the engine runs reasonably well, but you should repair it soon. Do not keep driving if the check engine light is flashing or the engine runs very rough.
What usually fixes P0308?
The most common fix is replacing the spark plug or ignition coil for cylinder 8. If that does not solve it, the injector, wiring, vacuum leaks, or compression should be checked.
Can a bad fuel injector cause P0308?
Yes. If cylinder 8 is not getting the right amount of fuel, it can misfire and trigger this code.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.