What it means
Misfires concentrated on cylinder 8. A cylinder-specific code points away from shared causes (fuel pressure, MAF) toward components dedicated to that cylinder — coil, spark plug, injector, compression.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine control module estimates misfires by tracking crankshaft speed changes as each cylinder fires. P0308 sets when those changes repeatedly indicate that cylinder 8 is not contributing normally, which can result from its ignition parts, injector, wiring, or compression.
Common causes
Most likely first.
- Faulty spark plug or ignition coil for cylinder 8
- Clogged or faulty cylinder 8 fuel injector
- Damaged wiring or connector at the cylinder 8 ignition or injector
- Low compression in cylinder 8
Symptoms
- Check engine light on or flashing
- Rough idle and uneven running
- Power loss, hesitation under acceleration
- Increased fuel consumption
- Possible smell of unburned fuel from exhaust
How to diagnose it
- Review freeze-frame data and live misfire counts to confirm when cylinder 8 misfires and whether the problem is limited to it.
- Inspect cylinder 8's spark plug, ignition coil, injector connector, and nearby wiring for damage, corrosion, or a poor connection.
- If parts are interchangeable, swap cylinder 8's coil or plug with another cylinder and check whether the misfire moves.
- Check cylinder 8 injector operation and wiring using the vehicle manufacturer's procedure.
- If the ignition and injector checks pass, perform a compression test and compare cylinder 8 with the others.
Common fixes
- Replace a worn or fouled cylinder 8 spark plug.
- Repair damaged or loose wiring at cylinder 8's coil or injector.
- Replace the cylinder 8 ignition coil if the misfire follows it during a swap.
- Clean or replace a clogged or faulty cylinder 8 injector.
- Repair the mechanical cause if cylinder 8 has low compression.
Can I keep driving?
A flashing check-engine light or severe rough running means you should stop as soon as it is safe, because an active cylinder 8 misfire can damage the catalytic converter. With a steady light and smooth running, limit driving and avoid heavy acceleration until the fault is checked.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.