Transmission Control Module (TCM)

Fig 1: Transmission Control Module (TCM)

Courtesy of GENERAL MOTORS COMPANY

The TCM (2) is mounted directly on top of the transmission (1). The selector lever is integrated in the control module. The TCM is mounted so that the selector lever shaft goes through the control module. The selector lever position is calibrated with a scan tool, there is no mechanical adjustment.

An exterior 16-pin connector connects to the car's electrical system. Underneath the control module is another connector (22-pin) that connects directly to the transmission. The TCM makes contact with all the transmission solenoids and sensors here.

NOTE: Magnetic fields from e.g. magnets and from high-current cables, such as starter cables and cables to auxiliary equipment, can interfere with the gear position sensor. A rule of thumb is max 1A per mm in distance from the control module. A starter cable carrying a current of 200A must therefore be kept at least 20 cm away from the control module.

The TCM has a microprocessor with clock, RAM memory and a programmable ROM. An internal bus connects the processor and memory with the I/O unit. The I/O unit reads values from the A/D converter for analogue inputs, digital inputs and bus, as well as activates the transistors' output stages.

Adaptive values are saved in a non-volatile memory (ROM). When changing transmission, these values must be zeroed using scan tool. After changing TCM they will be zeroed automatically after adding the control module using the scan tool.