P0306
HighP0306 — Cylinder 6 Misfire Detected
Description
What This Code Means
Code P0306 indicates a misfire in cylinder 6. The engine control unit (DME) monitors crankshaft speed irregularity and logs the fault when a misfire is detected. On N55 engines, ignition coils are prone to failure, especially at increased power levels (tuning). The system involves the ignition coil, spark plug, and fuel injector for cylinder 6.
Symptoms
Symptoms
- Engine: rough idle, vibration, power loss
- Indicators: Check Engine Light (CEL)
- Behavior: limp mode possible
Causes and fixes
Diagnosis and Repair
Step 1: Check the Ignition Coil
Swap the ignition coil from cylinder 6 to another cylinder. If the fault moves, the coil is bad. Replace it with an original (12138616153).
Step 2: Inspect the Spark Plug
Check the cylinder 6 spark plug. Replace if needed (part number 12120037563).
Step 3: Diagnose the Fuel Injector
Check the cylinder 6 fuel injector for clogging or leaks.
Step 4: Compression
If the previous steps don't find the cause, run a compression test to assess the cylinder's mechanical condition.
Possible secondary damage
Secondary Damage
Ignoring a misfire can lead to:
- Catalytic converter damage (unburned fuel)
- Oxygen sensor contamination
- Cylinder wall wear from uneven operation
Fix the cause as soon as possible to avoid expensive repairs.