P0305 on Infiniti: How to Diagnose & Fix
Cylinder 5 Misfire Detected
1 Infiniti model · 1 documented issue · $150-$900 repair
On Infiniti vehicles, P0305 (cylinder 5 misfire detected) is most often reported on the 2008-2013 Infiniti G37 as Ignition Coil Blistering and Failure Causing Cylinder Misfire (P0300-P0306) ($150-$900 repair). Replace the failed coil (and inspect all six for blistering); most shops replace all six with spark plugs once the first fails past 80k miles. Use OEM Hitachi coils—aftermarket units have a poor reputation on this engine. Each section below gives the symptoms, how to confirm the cause, the fix, parts and sources for that model.
Common causes of P0305 (all vehicles)
- Worn or fouled spark plug on cylinder 5
- Failed ignition coil or coil pack for cylinder 5
- Faulty or clogged fuel injector on cylinder 5
- Vacuum or intake air leak affecting that cylinder
- Bad spark plug wire or boot (on applicable engines)
- Low compression from worn rings, valves, or head gasket
- Carbon buildup or sticking valve on cylinder 5
- Lean or rich fuel condition affecting the cylinder
P0305 on Infiniti by model: symptoms, diagnosis and fix
The Hitachi coil-on-plug units on the VQ37VHR are a recurring failure item on higher-mileage G37s. Heat and electrical stress cause the coil body to blister or bulge, producing a random or single-cylinder misfire, rough idle and flashing check-engine light. Infiniti's bulletin ITB11-017A (cited by owners and parts guides) tells technicians that a P0300-P0306 misfire with a blistered, deformed or melted coil outer surface indicates coil failure. On the VQ37 the rear bank coils are buried under the intake plenum, which drives labor cost.
Common Symptoms
- Rough idle or shaking at idle
- Flashing check engine light under load
- Misfire counts on one or more cylinders
- Hesitation and power loss
How to Fix
Replace the failed coil (and inspect all six for blistering); most shops replace all six with spark plugs once the first fails past 80k miles. Use OEM Hitachi coils—aftermarket units have a poor reputation on this engine. If coils fail repeatedly, check engine grounds. No recall.
Looking for P0305 on a different make?
View P0305 across all makes →Frequently asked questions
What does P0305 mean on a Infiniti?
P0305 stands for "Cylinder 5 Misfire Detected." This code means the engine control module detected a misfire on cylinder number 5, meaning that cylinder is not burning its air-fuel mixture properly on some combustion cycles. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder fails to fire correctly. A misfire wastes fuel, can make the engine run rough or shake, and dumps unburned fuel into the exhaust, which can overheat and damage the catalytic converter. It generally points to a problem with spark, fuel delivery, or compression specifically affecting cylinder 5. On Infiniti it is documented across 1 model: G37.
How do I diagnose P0305 on a Infiniti G37?
Replace the failed coil (and inspect all six for blistering); most shops replace all six with spark plugs once the first fails past 80k miles. Use OEM Hitachi coils—aftermarket units have a poor reputation on this engine. If coils fail repeatedly, check engine grounds. Published repair guidance and available estimates are in the G37 section on this page.
What causes P0305 on Infiniti vehicles?
Documented causes on Infiniti: Ignition Coil Blistering and Failure Causing Cylinder Misfire (P0300-P0306). Generic causes of P0305: Worn or fouled spark plug on cylinder 5, Failed ignition coil or coil pack for cylinder 5, Faulty or clogged fuel injector on cylinder 5, Vacuum or intake air leak affecting that cylinder.
How much does it cost to fix P0305 on a Infiniti?
Published repair estimates on Infiniti range from $150 to $900 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.