P0303 tells you that your engine's control unit has detected repeated misfires specifically in cylinder 3. This code isolates the fault to that particular cylinder's spark plug, ignition coil, fuel injector, or internal compression, allowing a much more focused and efficient diagnosis than a random misfire code.
What does P0303 mean?
P0303 tells you that your engine's control unit has detected repeated misfires specifically in cylinder 3. This code isolates the fault to that particular cylinder's spark plug, ignition coil, fuel injector, or internal compression, allowing a much more focused and efficient diagnosis than a random misfire code.
P0303 is a misfire-related diagnostic trouble code classified as high severity. When your vehicle's ECU detects this condition, it stores P0303 and illuminates the check engine light.
What are the symptoms of P0303?
If your vehicle has triggered P0303, you may notice one or more of these symptoms:
Check engine light illuminated or flashing
Pronounced rough idle
Engine vibration, especially noticeable at low RPM
Power loss during acceleration
Higher than normal fuel consumption
Possible exhaust odour of unburned fuel
What causes P0303?
Here are the most common causes of P0303, ranked by how likely they are to be the culprit:
highWorn or fouled spark plug on cylinder 3
highFailed ignition coil on cylinder 3
mediumFaulty fuel injector on cylinder 3
mediumVacuum or intake gasket leak near cylinder 3
lowLow compression in cylinder 3 (worn piston rings, burnt valve)
Is it safe to drive with P0303?
No - address this immediately. Continued driving with a cylinder 3 misfire will send unburned fuel into the catalytic converter, potentially destroying it. Power loss may also create unsafe conditions in traffic. Repair promptly.
How do you diagnose P0303?
Follow these steps to pinpoint the root cause of P0303:
Scan for additional codes and review freeze-frame data for engine conditions at the time of the misfire
Swap the ignition coil from cylinder 3 to another cylinder, clear the codes, and drive. If the misfire moves with the coil, it is the cause
Pull the spark plug from cylinder 3 and inspect for abnormal wear, oil fouling, or incorrect gap. Replace if overdue or damaged
Test the fuel injector on cylinder 3 with a noid light to confirm electrical signal, and check spray pattern if accessible
Perform a compression test on cylinder 3 and a leak-down test if compression is low to determine whether the issue is valves, rings, or head gasket
How much does P0303 cost to fix?
Repair costs for P0303 vary depending on the root cause and your vehicle. Here are typical estimates:
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace spark plug (cylinder 3)
€5–€25
€30–€100
€35–€125
Easy
Replace ignition coil (cylinder 3)
€25–€130
€30–€100
€55–€230
Easy
Replace fuel injector (cylinder 3)
€50–€200
€60–€220
€110–€420
Moderate
Compression-related repair (valves, head gasket)
€150–€600
€400–€1300
€550–€1900
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0303 on specific vehicles
P0303 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
P0303 on BMW 3 Series
BMW 3 Series • 2006-2024
On the N52 and N54 engines, cylinder 3 is centrally located and tends to run hotter than outer cylinders, accelerating spark plug and coil wear. BMW recommends replacing plugs every 60,000 km and coils every 80,000 km as preventive maintenance.
What causes P0303 on a BMW 3 Series?
BMW 3 SeriesIgnition coil failure due to central cylinder heat on N52/N54
BMW 3 SeriesValve stem seal leaks on high-mileage N52 engines
P0303 repair cost for BMW 3 Series
Estimated costs for BMW 3 Series ownersadjusted higher than average due to BMW-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace spark plug (cylinder 3)
€7–€35
€42–€140
€49–€175
Easy
Replace ignition coil (cylinder 3)
€35–€182
€42–€140
€77–€322
Easy
Replace fuel injector (cylinder 3)
€70–€280
€84–€308
€154–€588
Moderate
Compression-related repair (valves, head gasket)
€210–€840
€560–€1820
€770–€2660
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0303 on Volkswagen Golf
Volkswagen Golf • 2005-2024
The EA888 2.0 TSI in Golf GTI models suffers from carbon buildup on intake valves. Cylinder 3 is commonly affected due to its position in the intake manifold flow path. Walnut blasting is the recommended remedy.
What causes P0303 on a Volkswagen Golf?
Volkswagen GolfCarbon buildup on cylinder 3 intake valve (EA888 direct injection)
Volkswagen GolfCoil pack failure on older 2.0 FSI models
P0303 repair cost for Volkswagen Golf
Estimated costs for Volkswagen Golf ownersadjusted higher than average due to Volkswagen-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace spark plug (cylinder 3)
€6–€29
€35–€115
€40–€144
Easy
Replace ignition coil (cylinder 3)
€29–€150
€35–€115
€63–€265
Easy
Replace fuel injector (cylinder 3)
€57–€230
€69–€253
€126–€483
Moderate
Compression-related repair (valves, head gasket)
€173–€690
€460–€1495
€633–€2185
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0303 on Toyota Yaris
Toyota Yaris • 2006-2024
The 1.0-litre 1KR-FE and 1.5-litre 1NZ-FE engines are generally reliable, but spark plugs that exceed the 80,000 km service interval frequently cause P0303 on cylinder 3. Toyota coils rarely fail, so the plug is almost always the cause.
What causes P0303 on a Toyota Yaris?
Toyota YarisSpark plugs overdue for replacement (past 80,000 km)
Toyota YarisInjector clogging from low-quality fuel
P0303 repair cost for Toyota Yaris
Estimated costs for Toyota Yaris ownersadjusted lower than average due to Toyota-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace spark plug (cylinder 3)
€4–€21
€26–€85
€30–€106
Easy
Replace ignition coil (cylinder 3)
€21–€111
€26–€85
€47–€196
Easy
Replace fuel injector (cylinder 3)
€43–€170
€51–€187
€94–€357
Moderate
Compression-related repair (valves, head gasket)
€128–€510
€340–€1105
€468–€1615
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0303 on Fiat 500
Fiat 500 • 2007-2024
The 0.9 TwinAir 2-cylinder does not have a cylinder 3, but the 1.2 Fire and 1.4 MultiAir 4-cylinder engines do. The 1.4 MultiAir is known for actuator solenoid issues that can cause misfires on specific cylinders including cylinder 3.
What causes P0303 on a Fiat 500?
Fiat 500MultiAir actuator solenoid failure on 1.4 engine
Fiat 500Ignition coil failure on 1.2 Fire engine
P0303 repair cost for Fiat 500
Estimated costs for Fiat 500 ownersadjusted lower than average due to Fiat-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace spark plug (cylinder 3)
€5–€24
€29–€95
€33–€119
Easy
Replace ignition coil (cylinder 3)
€24–€124
€29–€95
€52–€219
Easy
Replace fuel injector (cylinder 3)
€48–€190
€57–€209
€105–€399
Moderate
Compression-related repair (valves, head gasket)
€143–€570
€380–€1235
€523–€1805
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related diagnostic codes
These codes are often seen alongside P0303 or indicate related issues:
The most common causes are a worn spark plug or a failed ignition coil on cylinder 3. Less common but possible causes include a clogged fuel injector, a vacuum leak near that cylinder, or low compression from internal engine wear.
How do I know which cylinder is number 3?
Cylinder numbering depends on the engine layout. On inline-4 engines, cylinders are numbered 1-4 from the timing belt end. On V6 or V8 engines, check your service manual as bank and numbering conventions vary by manufacturer.
Can I just replace one spark plug to fix P0303?
Yes, you can replace only the cylinder 3 plug to fix the immediate issue. However, if one plug is worn, the others are likely in similar condition. Most mechanics recommend replacing the full set to prevent repeat visits.
Will P0303 clear itself after repair?
After fixing the cause, you can clear the code with a diagnostic scanner. Alternatively, the ECU will clear it automatically after several drive cycles with no misfires detected, but this can take days of normal driving.
Is P0303 serious?
Yes. Any single-cylinder misfire code should be treated urgently. A flashing check engine light means the misfire is severe enough to damage the catalytic converter. Even a steady light warrants prompt attention to avoid escalating repair costs.
