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 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.
If your vehicle has triggered P0303, you may notice one or more of these symptoms:
Here are the most common causes of P0303, ranked by how likely they are to be the culprit:
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.
Follow these steps to pinpoint the root cause of P0303:
Repair costs for P0303 vary depending on the root cause and your vehicle. Here are typical estimates:
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0303 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
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.
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.
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.
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.
Your car shakes at idle, under braking, or at 90 km/h. Here are the nine real causes, which ones an OBD2 scan reads, and what each repair costs.
Engine knocking ranges from a harmless cold-start lifter tick to rod knock that ends an engine. Here is how to tell them apart and what each fix costs.
Your car dies at every red light, then restarts fine. Here is what causes a car to shut off when you stop, how to find the fault, and what fixes cost.
Fixing a P0300 to P0304 misfire costs 40-250 euros for most cases. Here is how to tell which part failed - plug, coil, or injector - before paying for parts.
Your car logged P0303. Skanyx reads it on any standard Bluetooth OBD2 adapter, 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.
Download Skanyx