Control Module: Description and Operation

TCM
The Transmission Control Module (TCM) controls the operation of the transmission by deciding on the basis of a certain amount of information how the hydraulic system should be affected.

The information is obtained from a number of sensors and by communication with other systems in the car.

When the information has been processed, the TCM controls the shifting of gears, the lock-up function and the system pressure using 4 solenoids. Gear shifting is carried out using shift solenoids S1 and S2, the lock-up function by the torque converter clutch (TCC) solenoid (solenoid SL) and the system pressure by the pressure control solenoid ST.


CONTROL OF THE LOCK-UP FUNCTION
The lock-up function is controlled by the TCM switching the TCC solenoid on/off depending on the speed of the car and the opening of the throttle.
In the following cases the lock-up function is disconnected:
^ if an electrical fault occurs, so that limp-home is activated
^ when the brake light switch is activated and the input speed to the transmission is <2000 rpm
^ when the accelerator pedal is disengaged and the speed of the car is <125 km/h (78 mph) and the selector lever is in position D

CONTROL OF THE SYSTEM PRESSURE
The system pressure can be varied by the TCM switching on/off the pressure control solenoid.

When shifting gear N - R, the TCM lowers the system pressure with the help of the solenoid, in order to reduce any jerks from the shifting of gears.

When the fluid temperature is <10°C and the speed of the car is <5 km/h (3 mph) the TCM increases the system pressure with the help of the solenoid, in order to reduce the time taken to shift gears.
The function is disengaged in the following situations:
^ fluid temperature >20°C
^ speed of car >7 km/h (4 mph)
^ a change in the position of the selector lever

ELECTRONIC FAULT-TRACING
The TCM is also connected to the car's data link connector, which means that it is possible to carry out fault-tracing with ISAT.





TCM POWER SUPPLY
Battery Voltage +30
The TCM is continuously powered by battery voltage +30 on pin 18.
The TCM uses this voltage to maintain power to the memory. Power supply in stand-by position is less than 1 mA.

Battery Voltage +15
When the ignition key is in drive position the TCM receives +15 voltage on pin 17. The voltage is necessary to activate the system.





Grounding Points
The ground connections to pins 22 and 35 are internally connected in the TCM and are, electrically, the same point. The ground points have been duplicated in order to increase safety and functionality.

With the ignition in drive position it is possible to check the TCM's grounding points with the help of a voltmeter by measuring the voltage between pin 22 and the battery's negative terminal and between pin 35 and the battery's positive terminal.

In both cases the voltage should be less than 0.1 V