P0308: Cylinder 8 Misfire Detected

What does the P0308 error code mean?

The diagnostic trouble code P0308 means the car’s engine control module has identified a misfire in cylinder number 8. Shown on a scan tool, it’ll read as "Cylinder 8 Misfire Detected." A misfire can occur when the engine’s mix of air and fuel, ordinarily ignited by a spark plug, doesn’t ignite. The resulting “misfire” can affect engine performance and emissions.

Why is this issue important?

A misfire in any cylinder (though this code specifically indicates the eighth cylinder) can disrupt engine performance and lead to poor fuel economy. Your engine may feel down on power or suffer from increased exhaust emissions, which can lead to a damaged catalytic converter and a fuel smell — an indication that the car is running “rich” with too much fuel in its air-fuel mixture.

Can I safely drive my car with this error code?

You should not drive with an active misfire or the P0308 code. Your car will move under its own power with a misfire, but due to the delicate timing operation of your engine and its sensitive emissions parts, any of which could be damaged by a misfire, it can cause serious harm to the engine.

Common symptoms of the P0308 error code

• Rough idle
• Hesitation or jerking during acceleration
• Decreased engine power
• Poor fuel economy
• Illuminated check engine light
• Possible fuel smell from the exhaust or inside the car due to the engine running rich

How is the P0308 error code diagnosed?

• OBD-II scan: A scan tool can confirm the presence of P0308 and check for related codes.
• Visual inspection: Inspect the spark plug, ignition coil, and wiring for cylinder 8. Plugs on a misfiring cylinder will be excessively dirty.
• Compression test: Performed by a mechanic to verify the mechanical integrity of the cylinder.
• Fuel injector test: Ensure the injector for cylinder 8 is functioning correctly.
• Spark plug swap test: Swap over a spark plug and coil from a cylinder you know is properly firing, then allow the car to idle, determining if the misfire moves from cylinder to cylinder. If it does, the plug or coil is bad and needs replacement.

How is the P0308 error code repaired?

• Replace the spark plug in cylinder 8 if it is fouled or worn.
• Replace the ignition coil or coil pack for cylinder 8.
• Repair or replace damaged wiring or connectors to the ignition system.
• Clean or replace the fuel injector if it is clogged or malfunctioning.
• Address vacuum leaks or mechanical engine problems affecting cylinder 8.
• After repairs, remember to clear the code and perform a test drive to confirm it is gone.

Related reading

Follow the link below to reach our diagnostic check engine trouble codes catalog:
On-board diagnostics (OBD-II) trouble code directory