Transmission Control Module

The transmission control module (TCM) outputs signals to control the shift control solenoid valve and the EPRS to control the hydraulic operation of the transmission.

The transmission control module (TCM) processes signals from the transmission speed and temperature sensors, the selector lever, the engine control module (ECM) and other vehicle systems. From the received signal inputs and pre-programmed data, the transmission control module (TCM) calculates the correct gear, torque converter clutch setting and optimum pressure settings for gear shift and lock-up clutch control.

The engine control module (ECM) supplies the engine management data over the high speed controller area network (CAN) bus. The transmission control module (TCM) requires engine data to efficiently control the transmission operation, for example; flywheel torque, engine speed, accelerator pedal angle, engine temperature. The steering angle sensor and the anti-lock brake system (ABS) module also supply data to the transmission control module (TCM) on the high speed controller area network (CAN) bus. The transmission control module (TCM) uses data from these systems to suspend gear changes when the vehicle is cornering and/or the anti-lock brake system (ABS) module is controlling braking or traction control.

Using the signal inputs and the memorized data, the transmission control module (TCM) control program computes the correct gear and torque converter lock-up clutch setting and the optimum pressure settings for gear shift and lock-up clutch control. Special output-side modules (power output stages, current regulator circuits), allow the transmission control module (TCM) to control the solenoid valves and pressure regulators and consequently precisely control the hydraulics of the automatic transmission. In addition, the amount and duration of engine interventions are supplied to the engine management by way of the controller area network (CAN) bus.

The transmission control module (TCM) determines the position of the selector lever using signals from:

• The selector switch in the transmission.
• The park lock and M/S (manual/sport) 'CommandShift' switches on the selector lever.

When the driver operates the steering wheel paddle switches the selections are sensed by the transmission control module (TCM), which then operates in the manual CommandShift mode. If the selector lever is in D, the CommandShift mode is temporary and will cancel after a time period or can be cancelled by pressing and holding the + paddle for approximately 2 seconds. If the selector lever is in the M/S position, the CommandShift mode is permanent and can only be cancelled by pressing and holding the + paddle for approximately 2 seconds or by moving the selector lever to the D position.

The transmission control module (TCM) transmits the position of the selector lever and the selected gear on the high speed controller area network (CAN) bus. This information is shown in the gear selector display in the instrument cluster.

Engine Stall 

If the vehicle stalls it will coast down in gear, with the transmission providing drive to the engine. A restart can be attempted at this point and the engine may start and the driver can continue.

If the coast down speed reduces such that the speed of the engine is less than 600 rev/min, the transmission will go to neutral, D illumination will flash in the instrument cluster. The driver needs to select neutral or park and then press the brake pedal to restart the engine.

If the start/stop button is pressed when driving, the message ENGINE STOP BUTTON PRESSED is displayed in the message center but there will be no change to the ignition state. If the driver requires to switch off the engine, the start/stop button must be pressed for a second time. The engine will be stopped and will be back driven by the transmission as the vehicle coasts down.