The refined idle quality of your 2022 Mercedes-Benz C-Class has been replaced by an unsettling roughness, and the amber check engine light confirms something is amiss. A P0300 code—Random/Multiple Cylinder Misfire Detected—reveals the engine computer is detecting combustion problems, but unlike cylinder-specific codes, P0300 means the issue isn't isolated to one cylinder.
What Makes P0300 Different
While codes like P0301-P0304 point to specific cylinders, P0300 indicates misfires are occurring across multiple cylinders without a clear pattern. This is actually helpful diagnostically—it suggests a systemic problem rather than a single component failure.
Common Causes of Random Misfires in the M254 Engine
Your 2022 C-Class likely has the M254 mild-hybrid four-cylinder engine. Random misfires in this engine typically stem from:
- Fuel quality issues - Contaminated or low-octane fuel affects all cylinders equally
- Ignition coil degradation - Multiple coils can weaken simultaneously from age
- Spark plug wear - All four plugs installed at the same time wear at similar rates
- Vacuum leaks - Leaks in the intake system create lean conditions across all cylinders
- Mass airflow sensor malfunction - Incorrect air measurement affects engine-wide fuel delivery
- Low fuel pressure - Weak fuel pump affects all injectors equally
- EGR system issues - Excessive exhaust gas recirculation dilutes the air-fuel mixture
Diagnostic Approach for P0300
Since multiple cylinders are affected, focus on shared systems rather than individual components:
- Check freeze frame data to see conditions when the misfire occurred (engine temp, load, RPM)
- Monitor misfire counters for each cylinder—even with P0300, some cylinders may misfire more
- Inspect for vacuum leaks using smoke testing
- Verify fuel pressure at idle and under load
- Check MAF sensor readings against specifications
- Inspect spark plugs for consistent wear patterns
Fuel Quality: The Often-Overlooked Culprit
Before replacing any parts, consider recent fuel fill-ups. Did you use a different station? Get a lower grade than usual? Mercedes turbo engines are particularly sensitive to fuel quality. Try adding a tank of top-tier premium fuel and see if symptoms improve.
Repair Costs for 2022 C-Class P0300
- Spark plug replacement (all four): $250-$400
- Ignition coils (all four): $400-$700
- Vacuum leak repair: $150-$500
- MAF sensor replacement: $200-$400
- Fuel system cleaning: $150-$300