Transmission Control Module

Bosch manufactures the transmission control module, version GS 9.20, which has an 88-pin connector. The electronic transmission control module governs the following functions:

- Shift point control system
- Shift quality
- Converter Clutch
- Self diagnosis

The transmission control module requires the following signals (information) to determine the proper activation of the transmission solenoids and pressure regulators.

Transmission specific

Turbine speed
Output speed
Position P,R,N,D,4,3,2
Program switch (A or *)
Transmission temperature
Kick-down switch
Brake switch inputs

Engine specific

Engine speed
Battery voltage
Air mass measurement (load signal tL)
Engine temperature
Throttle valve angle
Injection time (ti)
Engine torque/engine torque reduction (ASR)

Engine/Transmission Control Module Communications

The transmission control module and engine control module are linked by a high speed databus known as the CAN (Controller Area Network) bus. The CAN bus allows a reduction in the number of individual wires used resulting in fewer connections and less material used in manufacture, while at the same time offering increased system reliability. The CAN bus consists of two shielded wires which link the engine and transmission control modules.





Figure 3 shows which information is shared by the engine and transmission control modules along the CAN bus. The data is transmitted in digital form; a "1" or "0" differentiated by either the presence or absence of a voltage. Previously, if the transmission control module was to receive data from the engine control module, the data was first converted into a different form of signal (i.e., a pulse of variable length and constant frequency). This conversion took place in the counter stage of the microprocessor with a driver stage finally sending out the signal. Once the signal arrived at the input circuit of the transmission control module, a counter stage would convert the signal back to digital form for use by the microprocessor. These data conversion processes and outside interference on the data line increased the possibility of a data transmission error. By transmifting the data in digital form over the CAN bus, the possibility for data transmission errors is greatly reduced.