What causes a cylinder 3 misfire?

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 the same age and have done the same work, so they are likely in similar condition. Replacing the full set costs little more in parts and saves stripping the same area again a few months later.

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.

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.

P0303: Cylinder 3 Misfire Detected

Quick Answer

Not safe to drive

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.

Severity: High · Misfire
Estimated repair cost: From €35 to €1900+, varies by vehicle

Scan your own car in about 60 seconds: see whether P0303 is really what it has, how urgent it is, and what the fix should cost. Free on iPhone and Android with an ELM327 adapter (Bluetooth LE on iPhone).

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What does P0303 mean?

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:

Worn or fouled spark plug on cylinder 3
: high
Failed ignition coil on cylinder 3
: high
Faulty fuel injector on cylinder 3
: medium
Vacuum or intake gasket leak near cylinder 3
: medium
Low compression in cylinder 3 (worn piston rings, burnt valve)
: low

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.

Full repair guides

Engines known for this code

P0303 on specific vehicles

P0303 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0303 on BMW

BMW 3 Series

See BMW-specific causes & cost

Volkswagen

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.

Toyota

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.

Fiat

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.

These codes are often seen alongside P0303 or indicate related issues:

Common questions about P0303

What causes a cylinder 3 misfire?: 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 the same age and have done the same work, so they are likely in similar condition. Replacing the full set costs little more in parts and saves stripping the same area again a few months later.
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.

Read our detailed guides

Scan your car with Skanyx to diagnose P0303

Your car logged P0303. Skanyx reads it on a standard OBD2 adapter (Bluetooth LE on iPhone), tells you whether it is safe to keep driving, and shows the €35-€1900 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.