Control Module
K71 Transmission Control Module
The TCM (2) is mounted directly on top of the transmission (1). The selector lever and transmission range sensor 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 external 16-terminal connector connects to the vehicle's electrical system. Underneath the control module is another connector (33-terminal) that connects directly to the transmission. The TCM makes contact with all the transmission solenoids and sensors here.
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 the transmission, these values must be zeroed using scan tool. The values are will be zeroed automatically after replacing the control module using the scan tool.
B182 Gear Shift Position Sensor
A non-contact type shift position sensor is integrated in the TCM. The sensor detects shift position by using a hall effect sensor, which outputs specified voltage according to the shift position (P, R, N, D). The magnet position in the sensor changes when moving the shift lever, enabling the hall effect sensor to convert magnetic field strength into an electrical signal according to the shift position.
B81 Park/Neutral Position Switch
The park/neutral position (PNP) switch is part of the K71 Transmission Control Module (TCM) assembly. The TCM provides a ground to the K20 Engine Control Module in park and neutral. The K20 ECM sends a 12V trace on the PNP circuit to the K71 TCM, used for circuit diagnostics. The PNP provides a range signal (permission to crank) to the ECM to enable engine start..