This article investigates common error codes associated with the E46 SMG pump due to its inability to generate the correct system pressure.
The error code, 56 (0x38), indicates the switching-on time of the hydraulic unit. Typically, the SMG pump is activated to prime the system until it reaches a specific pressure window. This usually happens when the vehicle has been parked for some time, and the door is opened. The pump’s activation noise is often heard as it primes the system. The bulk of this fluid pressure is stored in the accumulator, which supplies fluid as needed for various shifting and clutch operations before the electric motor/pump needs to reactivate. This error code arises when the DME determines that the pressure build-up to the minimum requirements is taking too long.
Several factors can contribute to this issue, listed in order of common failure:
1-Electric motor failure, where the motor provides low torque and doesn’t build pressure quickly enough. This will eventually lead to complete motor failure.
2-Damage to the high power relay (salmon relay), often related to item (1), where the extra load causes high current to wear out the relay. Over time, the relay becomes unreliable, not following DME instructions and staying in an ON or OFF position. This could trigger two specific codes.
When stuck in the ON position, it will cause the SMG pump to continuously run, overheat, and burn out the SMG pump motor (potentially triggering error code 54(0x36)). When stuck in the OFF position, it will prevent the SMG pump from priming to build up the required pressure (potentially triggering error code 53 (0x35)).
3-Low SMG fluid level, causing air to get into the pump and prohibiting pressure build-up. If this is the problem, bleeding the system is recommended to remove residual air in the hydraulic system.
4-External hydraulic system leaks causing fluid loss and low pressure. Check for leaks. Common areas include the SMG slave cylinder or actuator leak, which will allow the fluid level to decrease below the minimum.
5-Defective pressure sensor, causing an incorrect system pressure reading to the DME and causing the pump to activate more frequently than necessary.
6-Pressure accumulator not meeting specifications, not storing enough reserve pressure, causing the pump to activate more often to allow clutch/shift request initiation.
7-Damage to the wiring harness or fuse, which could occur if the relay is stuck ON, overheating the wiring harness, and damaging insulation.
8-Internal leak in the hydraulic system. Worn out parts in the SMG system will allow pressurized fluid to leak back into the reservoir. Some areas are solenoid valve seals, pressure relief valve, and solenoid valve damage.
