Ignition & misfire · Powertrain · generic (SAE-defined)
P0308: Cylinder 8 Misfire Detected
P0308 means the engine computer has logged repeated misfires in cylinder 8, usually on a V8, pointing to a spark, fuel, or mechanical problem there.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0308 sets
The powertrain control module (PCM) compares crankshaft speed between firing events and attributes missing power strokes to specific cylinders. Once cylinder 8 exceeds a manufacturer-set misfire count in its monitoring period, P0308 is set.
Common causes of P0308
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Failing coil or plug wire on cylinder 8
- Worn spark plug or plug damaged by heat
- Cylinder 8 injector restricted or not opening
- Plug wire touching exhaust manifold and arcing
- Vacuum leak near cylinder 8
- Low compression in cylinder 8
P0308 symptoms
- Check engine light on or flashing
- Rough idle or vibration
- Hesitation when accelerating
- Fuel smell or poor mileage
How P0308 is diagnosed
- Check freeze frame data and look for other codes.
- Inspect the cylinder 8 coil or plug wire for burns or damage from exhaust heat.
- Swap the coil or wire and plug with another cylinder to see if the misfire follows.
- Test the cylinder 8 injector and wiring.
- Check compression on cylinder 8 if the misfire stays put.
Typical fixes for P0308
- Replace the cylinder 8 coil or plug wire
- Replace spark plugs
- Reroute or shield plug wires away from exhaust heat
- Clean or replace the cylinder 8 injector
- Repair mechanical faults if needed
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0308 FAQ
What does code P0308 mean?
P0308 means the engine computer has logged repeated misfires in cylinder 8, usually on a V8, pointing to a spark, fuel, or mechanical problem there. The standard definition is "Cylinder 8 Misfire Detected."
Can I drive with a P0308 code?
Careful driving to a repair shop is usually fine while the light stays steady. If it flashes, the cylinder 8 misfire is heavy enough to damage the catalytic converter, so stop driving as soon as practical.
Why would a plug wire on cylinder 8 fail early?
On some V8 engines the rear cylinders run close to the exhaust manifold, and heat can damage plug wires or boots, leading to arcing and misfire.
Is P0308 only on V8 engines?
It applies to any engine with eight or more cylinders, which in practice means mostly V8s, plus V10 and V12 engines.
Keep researching
Engine guides by brand (known issues, specs)
More ignition & misfire codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.