Quick answer: The P0308 code indicates that your vehicle’s engine control module has detected a misfire in cylinder number 8. It affects the ignition and combustion system of your engine. This is a moderate to high-urgency issue that requires prompt attention to prevent permanent damage to your catalytic converter and engine internals.
If your dashboard is glowing with a flashing check engine light and your engine feels like it is stuttering or losing power, you are likely dealing with a P0308 code. This article explains exactly what this code means, why it happens, and the steps you should take to diagnose and resolve the issue without wasting money on unnecessary parts.
What Does P0308 Mean?
The P0308 code is a generic powertrain diagnostic trouble code. The “P” stands for powertrain, “03” refers to a misfire, and “08” identifies the specific cylinder. In any internal combustion engine, the computer monitors crankshaft speed; if it detects a momentary drop in speed that corresponds to the firing order of cylinder number 8, it triggers this code. Essentially, the fuel-air mixture in the eighth cylinder is not igniting properly, meaning that cylinder is not contributing its fair share of power to the engine.
Symptoms
- Noticeable engine hesitation or stumbling during acceleration.
- A rough, shaky idle when the vehicle is stopped.
- A significant loss of engine power under load.
- The “Check Engine” light blinking or remaining illuminated.
- Increased fuel consumption as the engine tries to compensate for the power loss.
- A raw fuel smell coming from the exhaust pipe.
Possible Causes
Many owners make the mistake of immediately replacing the ignition coils or fuel injectors. Always perform a proper diagnosis first to avoid spending money on parts that are not actually broken.
- Worn-out spark plugs or fouled spark plug electrodes.
- Damaged or frayed spark plug wires or ignition coil boots.
- A faulty ignition coil on cylinder 8.
- A clogged or malfunctioning fuel injector for cylinder 8.
- A vacuum leak near the intake manifold affecting the cylinder.
- Low engine compression due to internal mechanical wear or a burnt valve.
Check These Yourself Before Visiting a Mechanic
- Inspect the spark plug wire connected to cylinder 8 for any signs of cracking, burning, or loose connections.
- Check the ignition coil harness for any signs of corrosion or exposed wiring that might prevent the signal from reaching the coil.
- Listen for hissing noises around the intake manifold while the engine is running, which would indicate a vacuum leak.
How to Fix It
- Perform a spark test to ensure the coil is producing a strong spark.
- Remove and inspect the spark plug for cylinder 8; if it is carbon-fouled or electrode-worn, replace it.
- Swap the ignition coil from cylinder 8 with one from a different cylinder. If the misfire follows the coil to the new location, the coil is the culprit.
- Perform a fuel injector balance test to ensure the injector is delivering the correct amount of fuel.
- Conduct a compression test to rule out internal engine damage like a damaged piston ring or valve.
Estimated Repair Costs (2026)
| Job | Parts ($) | Labor ($) |
|---|---|---|
| Spark Plug Replacement | 15-30 | 50-150 |
| Ignition Coil Replacement | 50-150 | 50-100 |
| Fuel Injector Replacement | 100-300 | 100-300 |
| Compression/Internal Repair | 200-800 | 400-1,200 |
Note: these are 2026 estimates in US dollars; costs vary by make and model.
Frequently Asked Questions
Can I drive with the P0308 code?
You should avoid driving the vehicle as much as possible. A persistent misfire dumps raw, unburned fuel into the exhaust system, which can overheat and permanently destroy your expensive catalytic converter.
How do I clear the P0308 code?
You can clear the code using an OBD-II scanner, but it will return immediately if the underlying mechanical issue is not repaired. Clearing the code does not fix the misfire; it only hides the warning light temporarily.
Is cylinder 8 always the same location?
No, the location of cylinder 8 depends on your engine configuration. On V8 engines, the manual will specify the firing order and cylinder numbering. Always consult your service manual to ensure you are working on the correct cylinder.