900 Turbo Convertible L4-1985cc 2.0L DOHC Turbo EFI (1994)
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.
