Sevcontrol MOS90 631‑40056 is a DC traction and pump controller that uses the Sevcon MOS90 microprocessor architecture for motor drive applications. Common failure modes include power supply over‑voltage or ripple causing the controller to lock up, degraded MOSFETs leading to overheating and loss of torque, and firmware corruption resulting in error codes such as “E12” (motor driver fault) or “E22” (communication timeout). For this unit, first verify the input voltage meets the specified 48‑V DC range and check for excessive ripple with an oscilloscope; next inspect the MOSFETs and heat sink for signs of thermal damage or solder joint cracks; finally review the controller’s diagnostic LEDs or serial log for fault codes and reset the firmware if necessary.[oss-gpt-20b]