Transmission Control Systems: Description and Operation

Electronic System Description
The powertrain control module (PCM) and its input/output network control the following transmission operations:
^ Shift timing.
^ Line pressure (shift feel).
^ Torque converter clutch.

The transmission control is separate from the engine control strategy in the PCM, although some of the input signals are shared.

The PCM receives some input signals from engine-related sensors:
^ Mass air flow sensor (MAF sensor).
^ Engine coolant temperature sensor (ECT sensor).

These signals provide information to the PCM about the load and climate under which the engine is operating. Some other inputs are based on driver inputs, such as accelerator pedal position, which is sent to the PCM by the throttle position sensor (TP sensor). Still other inputs are provided by:
^ Transmission components.
^ Output shaft speed sensor.
^ Transmission range (TR) sensor (controlled by driver placement of the transmission range selector lever).
^ Transmission fluid temperature (TFT) sensor.

Using all of these input signals, the PCM can determine when the time and conditions are right for a shift or torque converter clutch (TCC) application. The PCM can also determine the line pressure needed to optimize shift feel. To accomplish these functions, the PCM controls four electronic solenoids:
^ Two on/off shift solenoids.
^ One pulse-width modulated torque converter clutch solenoid (TCC solenoid) for TCC control or "controlled slip," of the TCC.
^ An electronic pressure control (EPC) solenoid for line pressure control.

The PCM receives and sends electrical signals that are used to make the transmission more responsive to driver and vehicle needs.

The driver demands are transmitted to the PCM through four components:
^ Transmission range selector lever - The driver demand for a particular gear range is translated into an electrical signal for the powertrain control module by the transmission range (TR) sensor.
^ Accelerator pedal - The driver demand for torque and acceleration are sent mechanically to the throttle body on the engine. A throttle position sensor then translates this mechanical motion into an electrical signal and sends into the powertrain control module.
^ Brake pedal - A stoplight switch tells the powertrain control module when the brake is applied, indicating the driver demand to disengage the torque converter.
^ Transmission control switch - A momentary contact switch, located on the side of the transmission range selector that allows the driver to manually select three or four speed operation.