Worn, fouled or incorrectly gapped spark plug on cylinder 8; Faulty ignition coil or coil connector on cylinder 8; Faulty or blocked fuel injector on cylinder 8; Vacuum leak or intake leak affecting cylinder 8, such as a damaged intake manifold gasket; Low compression in cylinder 8 from a valve, piston ring or head gasket fault; Damaged wiring or poor connection to the coil or injector on cylinder 8; Internal engine fault such as a worn camshaft lobe or collapsed lifter, depending on engine design.

P0308

Cylinder 8 Misfire Detected.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
08: FaultThe specific fault in that area

What it means

P0308 means the engine control unit has detected misfiring on cylinder 8, so combustion in that cylinder is incomplete or absent. It sets when crankshaft speed monitoring shows repeated rotational speed drops attributed to that cylinder above a calibrated threshold. A flashing warning light means the misfire is severe enough to risk damaging the catalytic converter.

Symptoms

Engine warning light on or flashing
Rough idle and noticeable shaking
Hesitation, jerking or loss of power under acceleration
Smell of unburnt fuel from the exhaust
Poor fuel economy
Engine may be hard to start or may stall

Possible causes

Worn, fouled or incorrectly gapped spark plug on cylinder 8likely
Faulty ignition coil or coil connector on cylinder 8likely
Faulty or blocked fuel injector on cylinder 8possible
Vacuum leak or intake leak affecting cylinder 8, such as a damaged intake manifold gasketpossible
Low compression in cylinder 8 from a valve, piston ring or head gasket faultpossible
Damaged wiring or poor connection to the coil or injector on cylinder 8possible
Internal engine fault such as a worn camshaft lobe or collapsed lifter, depending on engine designrare

How to diagnose

Read freeze frame data to see load, rpm and temperature when the misfire set, and check for other stored codes, especially other misfire or fuel trim codes
Check live misfire counters to confirm the misfire is limited to cylinder 8 and whether it occurs at idle or under load
Inspect the coil, injector wiring and connectors on cylinder 8 for damage, corrosion, oil contamination or looseness
Remove and inspect the spark plug on cylinder 8 for wear, deposits, oil fouling and correct gap
Swap the cylinder 8 coil with a known good cylinder and see whether the misfire follows the coil
Test injector operation on cylinder 8 by checking its electrical signal, resistance and spray or flow
Check for intake leaks and inspect fuel trim data for signs of a lean condition
Carry out a compression or leak-down test on cylinder 8 if ignition and fuel faults are ruled out

How to fix

Replace the spark plug on cylinder 8, and usually the full set if they are due for replacement
Replace the faulty ignition coil on cylinder 8
Clean or replace the faulty fuel injector on cylinder 8
Repair or replace damaged wiring or connectors
Reseal or replace leaking intake gaskets or vacuum hoses
Carry out the necessary mechanical engine repair if compression testing finds a fault

Can I keep driving?

High severity

Avoid driving if the warning light is flashing, as unburnt fuel can quickly overheat and damage the catalytic converter. If the light is steady and the engine runs reasonably, drive gently and short distances only until it is repaired.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.