This article investigates a frequently occurring Error Code 55 (0x37) on the E46 SMG pump, which results from the pump’s inability to maintain the required system pressure.
The SMG pump usually activates to establish a specific pressure range, primarily noticeable when the vehicle has been stationary for a while. The pump primes the system upon opening the door, storing most of the fluid pressure in the accumulator for future shifting and clutch manoeuvres before needing reactivation. This error code surfaces when the DME calculates that the SMG pump is being switched on excessively over a short time span merely to meet minimum pressure requirements.
Several factors can contribute to this issue, listed below in order of commonality:
- Failing electric motor, causing low torque and slow pressure build-up, eventually resulting in complete motor failure.
- Damaged high power relay (salmon relay), often related to the first issue where additional load causes high current to wear out the relay. Over time, the relay becomes unreliable, causing two specific error codes based on its position.
- Low SMG fluid level, leading to air entering the pump and inhibiting pressure build-up. System bleeding is recommended if this problem occurs.
- External hydraulic system leak causing fluid loss and low pressure. Check for leaks, particularly in common areas like the SMG slave cylinder or actuator.
- Defective pressure sensor causing incorrect system pressure readings to DME, leading to unnecessary pump activation.
- Pressure accumulator not in spec, causing insufficient reserve pressure storage and more frequent pump activation.
- Damaged wiring harness or fuse, potentially from an overheating relay.
- Internal hydraulic system leak due to worn SMG system parts.
This detailed breakdown should help diagnose and rectify the E46 M3 SMG cog light error code 55 (0x37).
