The transmission control module (TCM) in a 1999 Mercedes-Benz ML320 is the main computer responsible for controlling the transmission. The TCM gathers data from all of the sensors in the transmission and makes decisions about when to actuate the switches and electronic servos inside the transmission. When the TCM fails, the transmission will operate erratically or cease to operate. Replacement TCM units are available from certified Mercedes-Benz dealerships.
Turn off the engine, shift the transmission into park and step down the parking brake. Turn on the interior dome light and open the driver's door.
Shine a work light above the pedal area on the driver's side. Pop loose the plastic trim panel to expose the electronic components near the steering column/pedal area.
Locate the TCM. It is mounted vertically to the underside of the dashboard, to the right of the steering column. It is a small, black box with two multi-wire connectors attached to it.
