Transmission Electronic Control System

Transmission Electronic Control System

Electronic System Description
The PCM and its input/output network control the following transmission operations:
^ Adaptive controls (model dependent)
^ 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. 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 inputs 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 best line pressure needed to optimize shift feel. To accomplish this, the PCM uses 6 output solenoids to control transmission operation.

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

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 electronic pressure control (EPC) pressures.

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 torque converter clutch (TCC) control.

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

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.

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, EPC pressure is adjusted to compensate for additional load on the engine.

Electronic Ignition (EI) System
The electronic ignition (EI) consists of a crankshaft position sensor, ignition coils and the PCM. 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, torque converter clutch control and EPC pressure.

Brake Pedal Position (BPP) Switch
The brake pedal position (BPP) switch tells the powertrain control module when the brakes are applied. The TCC disengages when the brakes are applied. The BPP switch closes when the brakes are applied and opens when they are released.

Transmission Control (TC) Switch
The transmission control (TC) switch is a momentary contact switch that allows the driver to cancel operation of 5th (overdrive) gear.

The TC switch is located on the end of the selector lever.

When the driver initially presses the TC switch a signal is sent to the PCM.

The PCM uses the shift solenoids to disengage/disable 5th gear operation and activate the coast clutch.

At the same time the PCM illuminates the transmission control indicator lamp (TCIL), to notify the driver that 5th gear is canceled.

When the TC switch is pressed again, 5th gear operation is enabled, the coast clutch is released and the TCIL is turned off.

Whenever the ignition is cycled (vehicle shut off then started again) the TC switch is turned off and 5th gear will be enabled, even if the TC switch had been on when the ignition was shut off.

Transmission Control Indicator Lamp (TCIL)
The transmission control indicator lamp (TCIL) is located in the instrument panel and is labeled O/D OFF. It is illuminated in conjunction with the TC switch.

The TCIL will flash if the EPC solenoid circuit is shorted or a fault has been detected in a monitored sensor used for transmission operation.

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 internally on the center support.

The PCM uses TSS information to help determine EPC and torque converter clutch (TCC) operation.

Four Wheel Drive (4WD) Low Switch
The four wheel drive (4WD) low range switch is located on the transfer case cover. It provides an indication of when the 4WD transfer case gear system is in the low range. The PCM then modifies the shift schedule for 4WD low transfer case gear ratio.

Output Shaft Speed (OSS) Sensor
The output shaft speed (OSS) sensor is a magnetic pickup, located at the park gear/trigger wheel assembly, that sends a signal to the PCM to indicate transmission output shaft speed. 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 intermediate shaft speed sensor is mounted externally on the center of the case.

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

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 and NEUTRAL, the back-up lamp circuit in REVERSE and the neutral sense circuit (4WD only) in NEUTRAL. 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, D, 2, 1).

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 varies with temperature. The PCM monitors the voltage signal across the TFT, and uses this information to determine the transmission fluid temperature.
^ The TFT is located on the main control body wiring harness assembly.
^ The PCM uses the TFT signal to help determine shift scheduling, torque converter clutch operation and EPC.

Electronic Pressure Control (EPC) Solenoid
The electronic pressure control (EPC) solenoid is a variable force style (VFS) solenoid. The VFS type solenoid is an electro-hydraulic actuator combining a solenoid and a regulating valve.

The PCM varies the current to the EPC solenoid.

This action causes the solenoid to regulate transmission line pressure and line modulator pressure. This is done by producing resisting forces to the main regulator and line modulator circuits. These 2 circuits control clutch application pressures.

The PCM has an adaptive learn strategy to electronically control the transmission which will automatically adjust the shift feel. When the battery has been disconnected or a new battery installed, certain transmission operating parameters may 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.

Shift Solenoids - A, B, C and D
Four On/Off shift solenoids allow the PCM to control shift scheduling.
^ The solenoids are 2-way, normally open style.
^ The shift solenoids (SSA, SSB, SSC and SSD) provide gear selection by controlling the pressures of the shift valves.
^ SSD is also used to apply and release the coast clutch.

Torque Converter Clutch (TCC) Solenoid
The torque converter clutch (TCC) solenoid is used to control the apply and release of the TCC.

PCM
The operation of the transmission is controlled by the PCM. Many input sensors provide information to the PCM. The PCM then controls actuators which determine transmission operation.