What does code P0303 mean on a Mercedes-Benz and is it safe to drive?
P0303: Cylinder 3 Misfire Detected. Here's what it means on your Mercedes-Benz, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
What this code means
The PCM has detected a misfire specifically on cylinder 3. Diagnosis follows the same steps as P0301—swap parts to the same position on a known-good cylinder to isolate the fault.
Common causes for your Mercedes-Benz
- Worn or fouled spark plug on cylinder 3
- Failing ignition coil on cylinder 3
- Leaking or clogged fuel injector
- Low compression on cylinder 3
Symptoms
- Check Engine Light, often flashing under load
- Rough idle or shaking
- Loss of power, hesitation
Typical fixes
- Replace spark plug and coil on cylinder 3
- Test and replace fuel injector
- Compression test if ignition parts don't resolve it
Repair cost range
For a Mercedes-Benz, repairs for P0303 often fall between $150 and $900, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Mercedes-Benz
Mercedes M272 P0303 on cylinder 3 (rear bank) can come from the balance shaft gear issue or a failed coil. Rear-bank coils on the M272 are harder to access. If the balance shaft timing is confirmed correct, swap the coil before further disassembly.
Most commonly affected models