Transmission Electronic Control System

Transmission Electronic Control System

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 strategy combined with the engine control provides optimum powertrain operation under all conditions. When determining the best operating strategy for transmission operation, the PCM uses input information from certain engine-related and driver-demand related sensors and switches.

In addition, the PCM receives input signals from certain transmission-related sensors and switches. The PCM also uses these signals when determining transmission operating strategy.

Using all of these input signals, the PCM can determine when the time and conditions are right for a shift, or when to apply or release the torque converter clutch. It will also determine the pressure needed to optimize shift feel. To accomplish this, the PCM uses 3 pressure controls, 1 torque converter clutch and 4 shift solenoids to control transmission operation.

The following provides a brief description of each of the sensors and actuators used to control transmission operation.

Powertrain Control Module (PCM)
The operation of the transmission is controlled by the powertrain control module (PCM). Many input sensors provide information to the PCM. The PCM then controls the actuators which determine transmission operation.

Air Conditioning (A/C) Clutch
An electromagnetic clutch is energized when the clutch cycling pressure switch closes. The switch is located on the suction accumulator/drier. The closing of the switch completes the circuit to the clutch and draws it into engagement with the compressor driveshaft. When the A/C is engaged, operating pressures are adjusted to compensate for additional load on the engine.

Brake Pedal Position (BPP) Switch
The brake pedal position (BPP) switch tells the PCM when the brakes are applied. The torque converter clutch disengages when the brakes are applied. The BPP switch closes when the brakes are applied and opens when they are released. The BPP is also used to disengage the brake shift interlock.

Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature (ECT) sensor detects engine coolant temperature and supplies the information to the PCM. The ECT sensor is used to control torque converter clutch (TCC) operation.

Electronic Ignition (EI) System
The electronic ignition (EI) system consists of a crankshaft position sensor, a pair of 4-tower ignition coils and the powertrain control module. The ignition control module operates by sending crankshaft position information from the crankshaft position sensor to the ignition control module. The ignition control module generates a profile ignition pickup (PIP) signal (engine rpm) and sends it to the PCM. The PCM uses PIP signal in the transmission strategy, wide-open throttle (WOT) shift control, TCC control, and operating pressures.

Intake Air Temperature (IAT) Sensor
The intake air temperature (IAT) sensor provides the sequential fuel injection (SFI) system mixture temperature information. The IAT sensor is used both as a density corrector for airflow calculation and to proportion cold enrichment fuel flow. The IAT sensor is installed in the air cleaner outlet tube. The IAT sensor is also used in determining control pressures.

Mass Air Flow (MAF) Sensor
The mass air flow (MAF) sensor measures the mass of air flowing into the engine. The MAF sensor output signal is used by the PCM to calculate injector pulse width. For transmission strategies, the MAF sensor is used to regulate electronic pressure control, shift and torque converter clutch scheduling.

Transmission Control (TC) Switch
The transmission control (TC) switch sends a signal to the PCM when the driver selects the D4 position, canceling operation of 5th (overdrive) gear.

The TC switch is located within the range selector assembly (base shifter only).

The PCM uses this signal to control the shift solenoids to disengage/disable 5th gear operation and activates coast clutch. At the same time, the PCM changes the instrument panel indicator to display D4.

When the driver moves the range selector lever back to the D5 position, 5th gear operation is enabled, the coast clutch is released and the instrument panel indicator changes to display D5.

Throttle Position (TP) Sensor
The throttle position (TP) sensor is a potentiometer mounted on the throttle body. The TP sensor detects the position of the throttle plate and sends this information to the PCM. The TP sensor is used for shift scheduling electronic pressure control and TCC control.

Digital Transmission Range (TR) Sensor
The digital transmission range (TR) sensor is located on the outside of the transmission at the manual lever. The digital TR sensor completes the start circuit in PARK, NEUTRAL, and the back-up lamp circuit in REVERSE. The digital TR sensor also opens and closes a set of 4 switches that are monitored by the PCM to determine the position of the manual lever (P, R, N, D5, 3, 2, 1).

Turbine Shaft Speed (TSS) Sensor
The turbine shaft speed (TSS) sensor is a magnetic pickup that sends the PCM torque converter turbine speed information.

The TSS sensor is mounted externally on the case.

The PCM uses TSS information to help determine appropriate operating pressures and TCC operation.

Output Shaft Speed (OSS) Sensor
The output shaft speed (OSS) sensor is a magnetic pickup, located at the park gear, that sends a signal to the PCM to indicate transmission output shaft speed. The OSS sensor is mounted externally on the case. The OSS is used for torque converter clutch control, speed scheduling and to determine electronic pressure control.

Intermediate Shaft Speed Sensor
The intermediate shaft speed sensor is a magnetic pickup that sends planetary sun gear speed information to the PCM. The sensor is mounted externally on the center of the case.

The PCM uses the sensor information to aid in determining pressure requirements.

Pressure Control Solenoids (PCA, PCB, PCC)
The pressure control (PC) solenoids are a variable-force style (VFS) solenoid. The VFS-type solenoid is an electrohydraulic actuator combining a solenoid and a regulating valve.

The line pressure tap is used to verify output pressure from PC A or PC B by turning either one OFF, while verifying the output from the other solenoid. The second pressure tap is used to verify the output from the PC C solenoid.

There are 3 PC solenoids located in the solenoid body assembly used to control line pressure, band and clutch application pressure within the transmission.

The PCM varies the current to the PC solenoid.

The PCM has an adaptive learn strategy to electronically control the transmission which will automatically adjust the shift feel. When the battery is disconnected or a new battery installed, certain transmission operating parameters can be lost. The PCM must relearn these parameters. During this learning process, you may experience slightly firm shifts, delayed or early shifts. This operation is considered normal and will not affect the function of the transmission. Normal operation will return once these parameters are stored by the PCM.

Torque Converter Clutch (TCC) Solenoid
The torque converter clutch (TCC) solenoid is a pulse width modulating-type solenoid that is used to control the apply and release of the TCC.

Shift Solenoids - (SSA, SSB, SSC, SSD)
Four ON/OFF shift solenoids allow the PCM to control shift scheduling.
^ The solenoids are 3-way, normally open style.
^ The shift solenoids SSA, SSB, SSC and SSD provide gear selection of 1st through 5th and reverse gears by directing PC pressures to the appropriate elements.

Coast braking and manual gears are also controlled by the shift solenoids.

Transmission Fluid Temperature (TFT) Sensor
^ The transmission fluid temperature (TFT) sensor is a thermistor-type sensor that varies a reference voltage signal. The resistance in the TFT sensor varies with temperature. The PCM monitors the voltage signal across the TFT sensor, and uses this information to determine the transmission fluid temperature.
^ The TFT sensor is located on the solenoid body.
^ The PCM uses the TFT sensor signal to help determine shift scheduling, torque converter clutch operation and pressure control requirements.

It sends a voltage signal to the PCM The voltage signal varies with transmission fluid temperature. The PCM uses this signal to determine whether a cold start shift schedule is necessary. The shift schedule is compensated when the transmission fluid temperature is cold. The PCM also inhibits TCC operation at low transmission fluid temperatures and determines PC solenoid operations.

Accelerator Pedal Position (APP) Sensor
The accelerator pedal position (APP) sensor is mounted on the accelerator pedal. The APP sensor detects the position of the accelerator pedal and inputs this information as a voltage to the PCM. The PCM uses the APP sensor information to aid in determining shift scheduling electronic pressure control (EPC) and torque converter control.

Instrument Panel Range Selector Indicator
This indicator is an electronic readout in the instrument cluster which will match the position of the range selector (P, R, N, D5, D4, 3, 2, 1). If an error in the range selector assembly occurs, an "E" (error) will be displayed on the instrument panel.

Select Shift Transmission (SST) Switches (+ and -)
The positions indicated by a (+) or a (-) allow the driver to manually select the appropriate upshift (+) or downshift (-) and gear range.

The select shift transmission (SST) switches are located within the transmission range selector assembly and are momentary contact switches that send a signal to the PCM each time the driver moves the selector lever into the upshift or downshift gear range.

The PCM uses the input signals from the SST+ and the SST- switches, along with other vehicle inputs to determine which gear should be commanded.