P0303 on Alfa Romeo
Cylinder 3 Misfire Detected
P0303 on Alfa Romeo vehicles indicates cylinder 3 misfire detected. Au7o has documented this code across 1 Alfa Romeo model — most commonly on Stelvio. 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. Typical repair costs on Alfa Romeo range from $500 to $1,200, depending on the specific model and root cause.
Common 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
- •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 Alfa Romeo by Model
Alfa Romeo Stelvio(1 issue)
- 2.0L Turbo Intake Valve Carbon Buildup Causing Cold-Start Misfire2018-2026
The 2.0L GME turbo four is direct injected, so no fuel washes over the back of the intake valves. Crankcase vapour routed through the PCV system bakes onto the valve heads and forms hard carbon deposits that disrupt airflow and seal quality. What makes the Stelvio case notable is how early it appears: Stelvio and Giulia forum members report being sent for walnut blasting at Alfa's direction at roughly 6,000-6,500 miles because of cold-start misfires, an order of magnitude sooner than the 75,000-125,000 mile window typical of other direct-injection engines. Symptoms are worst on a cold start and often clear once the engine warms, which is why the condition is frequently dismissed on a test drive. This is a 2.0L issue and should not be merged with the 2.9L V6 Quadrifoglio's separate intake-side story.
Looking for P0303 on a different make?
View P0303 across all makes →Frequently Asked Questions
What does P0303 mean on Alfa Romeo?▼
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 Alfa Romeo specifically, this code is documented across 1 model.
What causes P0303 on Alfa Romeo vehicles?▼
Common causes on Alfa Romeo: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0303 on a Alfa Romeo?▼
Repair costs on Alfa Romeo range from $500 to $1,200, depending on the specific model and root cause.
Which Alfa Romeo models have P0303 documented?▼
Au7o has documented P0303 on 1 Alfa Romeo model: Stelvio.