TCM Transmission Control Module
The (TCM) transmission control module can be a standalone controller or located in the (PCM) powertrain control module. The TCM receives input from various sensors and then uses this information to activate the (TCC) torque converter clutch, control line pressure and provide smooth shift timing. The TCM has preset data to compare these inputs and make the appropriate decision.
The TCM receives information from sensors located in the transmission as well as a few shared over the multiplex network with the PCM. Sensors detect conditions such as movement or pressure and convert them into an electrical signal for the TCM.
Automatic transmission input sensors include the:
Brake switch: The brake switch signals the computer when the brakes are applied. The TCM uses this signal to control the TCC.
ECT: The engine coolant temperature sensor monitors engine coolant temperature. The TCM uses this input to delay TCC application until the engine reaches operating temperature.
MAF: The mass air flow sensor informs the PCM of engine load. It senses the mass of air flow in the air tube before it enters the intake manifold. The TCM uses this information for shift timing, line pressure and TCC application.
TPS: The throttle position sensor informs the PCM of throttle angle. The TCM uses this information to control shift timing. At (WOT) wide open throttle the TCM will initiate a downshift.
TFT: The transmission fluid temperature sensor is located inside the transmission. The TCM uses this information to monitor the transmission’s fluid temperature.
TSS: The turbine shaft speed sensor informs the TCM of turbine shaft speed.
OSS: The output shaft speed sensor informs the TCM of output shaft speed. This can be compared with vehicle speed sensor's signal to monitor performance.
Pressure Sensors: The TCM uses these sensors to verify that the desired hydraulic circuit is under pressure.
The TCM uses these inputs to make decisions and activate actuators like shift solenoids, the TCC solenoid, EPS solenoid, and coast-timing solenoids.