P0305
HighP0305 — Cylinder 5 Misfire Detected
Description
What This Code Means
Code P0305 indicates a misfire in cylinder 5. The engine control unit (DME) monitors crankshaft rotational irregularity and logs the fault when misfires are detected. On N55 engines, one of the common causes is ignition coil failure from thermal stress. Spark plug or injector faults are also possible.
Symptoms
Symptoms
- Engine: rough idle, vibration, loss of power
- Indicators: Check Engine Light (CEL) on or flashing
- Behavior: may drop into limp mode
Causes and fixes
Diagnosis and Repair
Step 1: Check the Ignition Coil
Swap the ignition coil from cylinder 5 to another cylinder. If the fault moves with it, replace the coil (OEM 12138616153).
Step 2: Check the Spark Plug
Inspect the cylinder 5 spark plug (OEM 12120037563). Replace it if worn or fouled.
Step 3: Check the Injector
Check the cylinder 5 injector for clogging or failure.
Step 4: Compression Test
If the steps above turn up nothing, run a compression test to assess the cylinder's mechanical condition.
Possible secondary damage
Secondary Damage
Ignoring the fault can lead to:
- Catalytic converter damage from unburned fuel
- Contaminated oxygen sensors
- Cylinder wall wear from an unstable idle
Fix the fault as soon as possible to avoid expensive repairs.