What is the DSM / ISM
DSM and ISM are electronic modules that, on command from the selector lever, physically move the transmission into P, R, N and D and engage the parking lock. They consist of an electric motor, a mechanism and an electronic circuit board, and are mounted directly on the transmission.
Symptoms
- The transmission won't come out of P or won't go into it
- The gear position indicator flashes on the instrument cluster
- Transmission error message and a warning to secure the vehicle
- The vehicle won't move even though the engine is running
Most common causes
Because of where it sits on the transmission, the module is exposed to moisture and heat. Common problems are corrosion of the board and connectors, a worn electric motor or mechanism, and software faults.
How we fix it
- Diagnostics tell us whether the fault is in the module, the selector lever or the transmission control unit
- We test the module on the test bench
- We repair the electronic board and the mechanism
- We reprogram and adapt a new or used module to the vehicle
