Transmission Control Systems: Description and Operation

DESCRIPTION
The powertrain control module (PCM) and its input/output network control the following transaxle operations:
^ shift scheduling
^ fine pressure (shift feel)
^ torque converter clutch scheduling
^ coast braking
The transaxle control is separate from the engine control strategy in the PCM, although some of the input signals are shared.

POWERTRAIN CONTROL MODULE INPUT SIGNALS
The PCM receives input signals from the following engine-related sensors as well as the electronic ignition (EI) system:
^ mass air flow sensor (MAP)
^ engine coolant temperature sensor (ECT)
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 relayed to the PCM by the throttle position sensor (TP sensor). Still other inputs are provided by the following:
^ vehicle speed signal from anti-lock brake system
^ Brake On/Off (BOO) switch
^ turbine shaft speed (TSS) sensor
^ air conditioning clutch (A/C clutch)
^ power steering pressure (PSP) switch
^ transaxle range (TR) sensor (controlled by the driver placement of the transaxle range selector lever)
^ transaxle fluid temperature (TFT) sensor

POWERTRAIN CONTROL MODULE OUTPUT SIGNALS
Using all of the input signals, the PCM can determine when to schedule a shift or torque converter clutch application. The PCM can also determine the line pressure needed to optimize shift feel. To accomplish these functions, the PCM controls five electronic solenoids:
^ three on/off shift solenoids
^ one pulse-width modulated torque converter clutch solenoid (TCC solenoid) for torque converter clutch (TCC) control
^ an electronic pressure control (EPC) solenoid for line pressure control

POWERTRAIN CONTROL MODULE FAULT DETECTION
The PCM also has the ability to:
^ monitor its input and output devices for the presence of faults.
^ store diagnostic trouble codes (DTCs) related to detected faults.
^ alert the driver for some detected faults by turning on the malfunction indicator lamp (MIL) in the instrument cluster.
^ display information when a service technician connects diagnostic equipment.

DRIVER INPUTS
The PCM receives and sends electrical signals that are used to make the transaxle more responsive to driver and vehicle needs. The driver demands are transmitted to the PCM through three components:
Transaxle Range Selector Lever:
The driver's demand for a particular gear range is translated into an electrical signal for the PCM by the TR sensor.
Accelerator Pedal Shaft Lever:
The driver's 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 that is monitored by the PCM.
Brake Pedal:
A Brake On/Off (BOO) switch tells the PCM when the brake is applied, indicating the driver demand to disengage the torque converter.