Components Description

TRANSMISSION CONTROL COMPONENTS:

The mechanical operation of the transmission follows conventional epicyclic gear transmission operation. The components unique to the electronic control of the transmission are explained here.




Transmission control module (TCM): The TCM is a microprocessor based unit having control over all shift points and the transmission line pressure that determines shift quality. Control inputs are applied to the transmission operating strategy. From the strategy, the TCM controls the shift solenoids, force motor (line pressure), and the torque converter clutch solenoid. A diagnostic facility allows the TCM to diagnose transmission and related component problems. This information is accessed via serial communication.

NOTE: The TCM location varies with vehicle model type.







Pressure switch manifold: The pressure switch manifold is a multiple switch assembly made up of 5 normally-open pressure switches to provide a logic input to the TCM. Various fluid pressures are fed from the manual valve to the switches depending on gear selector and manual valve positioning. These pressures determine the digital logic at the connector pins A, B and C.







Transmission output speed sensor: The output speed sensor is a variable reluctance magnetic pick-up. The sensor is mounted in the case opposite the output speed sensor ring that is pressed on to the output carrier assembly. Whenever the vehicle is moving, the sensor produces an AC voltage input to the TCM proportional to vehicle speed.







Transmission input speed sensor: The input speed sensor is identical to the output speed sensor except that it uses the machined teeth on the forward clutch housing as the rotor. The sensor produces an AC voltage input to the TCM proportional to torque converter turbine speed.




Fluid Temperature sensor: The transmission fluid temperature sensor, located in the pressure switch wiring harness, is a temperature sensitive resistor (thermistor) that provides a fluid temperature input to the TCM.







Shift solenoids: Two shift solenoids - A and B - are used to apply upshifts and downshifts in all forward gear ranges. The solenoids work together in a combination of ON and OFF sequences to apply hydraulic pressure to the various shift valves.







Torque converter clutch (TCC) solenoid: The TCC solenoid is used to control the torque converter lock-up clutch apply and release. The solenoid duty cycle (percent time energized) is varied by TCM control of the ground circuit. The variable duty cycle of the solenoid allows the lock-up rate to be varied to ensure smooth operation.







Force motor: The force motor is an electronic pressure regulator controlled by the TCM to produce a hydraulic "torque signal pressure" that is primarily an indication of throttle opening. The duty cycle (percent time energized) of the force motor is regulated by TCM control of supply current. No current flow applies maximum torque signal pressure, maximum current flow applies minimum torque signal pressure. Torque signal pressure controls transmission main line pressure at the pressure regulator valve accordingly.




[1][2]Throttle position sensor: The twin track throttle position sensor is mounted under the throttle turntable. The throttle position input to the TCM is an approximation of engine torque.




Barometric pressure sensor: A barometric pressure sensor, located under the right front component panel (right front inner fender), provides an air density signal to the TCM.