P0308
Cylinder 8 Misfire DetectedP0308 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 8 Misfire Detected. It is logged by the engine control unit when the misfire monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0308 means
P0308 is an SAE generic powertrain code set by the Engine Control Module (ECM) when it detects a misfire condition in cylinder number 8. The ECM monitors crankshaft speed fluctuations via the crankshaft position sensor; a misfire causes a measurable deceleration event on the firing stroke of the affected cylinder. On V8 engines cylinder 8 fires once every 720° of crankshaft rotation, so the ECM has clear windows to isolate which cylinder is misfiring. This code is physically impossible on engines with fewer than eight cylinders and is therefore exclusive to V8, V10, and V12 configurations.
The severity depends heavily on the cause and duration. A single isolated misfire may set a pending code and illuminate the MIL, while a sustained or severe misfire will trigger a flashing MIL — the SAE J1930 signal for catalytic converter damage risk — and may engage a fuel cut on the offending cylinder to protect the catalyst from unburned fuel igniting in the exhaust. If left unaddressed, raw hydrocarbons washing the cylinder walls will dilute engine oil and accelerate wear.
Common root causes are divided between ignition, fuel delivery, and mechanical compression faults. On individual-coil (COP) engines, swapping the coil and spark plug from cylinder 8 to a known-good cylinder is the fastest first diagnostic step: if the misfire follows the part, the part is at fault; if it stays on cylinder 8, the fault is in the injector, low compression, or wiring harness branch feeding that cylinder.
Common causes
Most-frequently reported root causes when P0308 is logged.
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1
Faulty or worn spark plug on cylinder 8
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2
Failed or weak ignition coil (COP) on cylinder 8
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3
Clogged or failed fuel injector on cylinder 8
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4
Low compression on cylinder 8 (worn rings, burnt valve, damaged head gasket)
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5
Lean fuel condition specific to cylinder 8 (intake manifold vacuum leak near that runner)
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6
Contaminated engine oil (oil fouling plug/coil boot after valve-seal failure)
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7
Crankshaft or camshaft position sensor signal noise causing false cylinder assignment
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8
PCM/ECM software fault or hardware failure (rare)
Symptoms drivers notice
How to diagnose P0308
A typical diagnostic flow when this code is present.
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1
Connect a scan tool, record freeze-frame data, and confirm the misfire counter is incrementing on cylinder 8 specifically
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2
Inspect the spark plug on cylinder 8 for fouling, gap erosion, cracks, or oil contamination
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3
Swap the cylinder 8 COP coil and plug with a known-good cylinder and re-test — if the misfire moves, replace those parts
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4
Perform a relative compression test or cylinder-specific power balance test to rule out low compression
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5
Check the cylinder 8 injector with a noid light and/or injector balance test; listen for injector click with a mechanic's stethoscope
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6
Inspect the wiring harness connector at the cylinder 8 coil and injector for corrosion, chafing, or pull-out pins
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7
If compression is low, perform a wet compression test and leak-down test to distinguish rings from valves; escalate to cylinder head inspection if needed
Related powertrain codes
Frequently asked questions
Can P0308 damage the catalytic converter?
Yes. Unburned fuel from a misfiring cylinder enters the exhaust and can ignite inside the catalytic converter, causing thermal damage or complete destruction. A flashing MIL is the ECM's warning that this is happening — stop driving and diagnose immediately.
Why does P0308 only appear on certain engine types?
Cylinder 8 only exists on engines with eight or more cylinders (V8, V10, V12, flat-8, etc.). A four- or six-cylinder engine physically cannot set this code; if a scanner reports it on such an engine, suspect a wiring fault, scan tool error, or incorrect ECM flash.
Is it safe to drive with P0308?
If the MIL is steady and drivability is only mildly affected, short-distance driving to a workshop is generally acceptable. If the MIL is flashing, reduce load immediately (no hard acceleration, no towing) and seek repair urgently to avoid catalyst damage and potential engine harm.
Could P0308 be caused by bad fuel?
Contaminated or very low-octane fuel can cause misfires, but it would typically cause misfires on multiple cylinders rather than isolating to cylinder 8. If all cylinders show elevated misfire counts after a fuel fill, suspect fuel quality. A cylinder-8-only misfire points toward a part or mechanical fault specific to that cylinder.
Disabling P0308 in software
RaceTune can permanently disable P0308 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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