P0303 on Infiniti: How to Diagnose & Fix
Cylinder 3 Misfire Detected
1 Infiniti model · 1 documented issue · $150-$900 repair
On Infiniti vehicles, P0303 (cylinder 3 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 P0303 (all vehicles)
- Worn or fouled spark plug in cylinder 3
- Failed or weak ignition coil on cylinder 3
- Bad spark plug wire or boot (where applicable)
- Clogged or leaking fuel injector for cylinder 3
- Vacuum or intake air leak affecting that cylinder
- Low compression (worn rings, burnt/leaking valve, head gasket)
- Wiring or connector fault at the coil or injector
P0303 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 P0303 on a different make?
View P0303 across all makes →Frequently asked questions
What does P0303 mean on a Infiniti?
P0303 stands for "Cylinder 3 Misfire Detected." This code means your engine's computer detected a misfire specifically in cylinder number 3 — that cylinder isn't burning its fuel-air mixture properly or completely. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder is supposed to fire. A misfire wastes fuel, can cause a noticeable shake, rough idle or loss of power, and can flood raw fuel into the exhaust where it may overheat and damage the catalytic converter. Because the fault is isolated to one cylinder, the cause is usually something specific to that cylinder's ignition, fuel delivery, or compression. On Infiniti it is documented across 1 model: G37.
How do I diagnose P0303 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 P0303 on Infiniti vehicles?
Documented causes on Infiniti: Ignition Coil Blistering and Failure Causing Cylinder Misfire (P0300-P0306). Generic causes of P0303: Worn or fouled spark plug in cylinder 3, Failed or weak ignition coil on cylinder 3, Bad spark plug wire or boot (where applicable), Clogged or leaking fuel injector for cylinder 3.
How much does it cost to fix P0303 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.