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 (TCC)
The transmission control strategy is separate from the engine control strategy within the PCM, although some of the input signals are shared. When determining the best operating strategy for transmission operation, the PCM uses certain inputs from engine-related and driver-demand related sensors and switches.
In addition, the PCM receives inputs from transmission-related sensors and switches. The PCM also uses these signals when determining transmission operating strategy.
Using these inputs, the PCM can determine when the time and conditions are right for a shift or when to apply or release the TCC. It will also determine the best line pressure needed to optimize shift feel. To accomplish this, the PCM uses 6 solenoids to control transmission operation.
The following provides a brief description of the input sensors and solenoids used to control transmission operation.
Intake Air Temperature (IAT) Sensor
The Intake Air Temperature (IAT) sensor provides an electrical input to the PCM corresponding to intake air temperature. The IAT sensor is used in determining Electronic Pressure Control (EPC) solenoid control which is used to control line pressure. The IAT sensor is part of the Mass Air Flow (MAF) sensor.
Throttle Position (TP) Sensor
The Throttle Position (TP) sensor is a potentiometer mounted on the Throttle Body (TB). 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, EPC solenoid control and TCC scheduling.
Engine Coolant Temperature (ECT) Sensor
The Engine Coolant Temperature (ECT) sensor is a thermistor device in which resistance changes with temperature change. The electrical resistance of a thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor and provides electrical signals to the PCM corresponding to temperature. The ECT sensor is used to control TCC scheduling.
Mass Air Flow (MAF) Sensor
The Mass Air Flow (MAF) sensor measures the speed and density 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 EPC, shift and TCC scheduling.
A/C Clutch
An electromagnetic clutch is energized when the A/C cycling switch closes. The pressure switch is located on top of the suction accumulator. When the A/C cycling switch contacts close this completes the circuit to the clutch and draws it into engagement with the compressor driveshaft. When the A/C is engaged, EPC solenoid control is adjusted by the PCM to compensate for additional load on the engine.
Electronic Ignition (EI) System
The Electronic Ignition (EI) consists of a Crankshaft Position (CKP) sensor, ignition coils and the PCM. The ignition control module operates by sending CKP information from the CKP sensor to the ignition control module. The ignition control module generates a profile ignition pickup signal (engine rpm) and sends it to the PCM. The PCM uses profile ignition pickup signal in the transmission strategy, Wide Open Throttle (WOT) shift control, TCC scheduling and EPC solenoid control.
Brake Pedal Position (BPP) Switch
The Brake Pedal Position (BPP) switch sends a signal to the PCM indicating when the brake pedal is applied. The TCC will disengage 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 gear.
The TC switch is located on the end of the selector lever.
When the TC switch is pressed, a signal is sent to the PCM.
The PCM commands 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 cancelled.
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 (engine turned off then started again) the TC switch command is turned off and 5th gear will be enabled, even if the TC switch command was on when the ignition was shut off.
Transmission Control Indicator Lamp (TCIL)
The TCIL is located in the Instrument Cluster (IC) and is labeled Overdrive (O/D) OFF. It is illuminated in conjunction with the TC switch.
The TCIL will flash if the EPC 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 a signal to the PCM to indicate transmission turbine shaft rpm.
The TSS sensor is mounted internally on the center support.
The PCM uses TSS information to help determine EPC solenoid control and TCC scheduling.
Four-Wheel Drive (4WD) Low Switch
The Four-Wheel Drive (4WD) low 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 OSS. The OSS sensor is used for TCC scheduling, speed signal and to determine EPC solenoid control.
Intermediate Shaft Speed Sensor
The intermediate shaft speed sensor is a magnetic pickup that sends a signal to the PCM to indicate planetary sun gear speed information. 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.
Transmission Range (TR) Sensor
The Transmission Range (TR) sensor is located on the outside of the transmission at the manual lever. The 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 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 device in which resistance changes with temperature change. The electrical resistance of the TFT sensor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the TFT sensor and provides an electrical signal to the PCM corresponding to temperature. The PCM monitors the voltage signal across the TFT sensor and uses this information to determine the TFT.
The TFT sensor is located on the transmission internal harness.
The PCM uses the TFT sensor signal to help determine shift timing, TCC scheduling and EPC solenoid control.
Electronic Pressure Control (EPC) Solenoid
The EPC solenoid is a Variable Force Solenoid (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.
Shift Solenoids - Shift Solenoid A (SSA), Shift Solenoid B (SSB), Shift Solenoid C (SSC) and Shift Solenoid D (SSD)
Four On/Off shift solenoids allow the PCM to control shift timing.
The solenoids are 2-way, normally open style.
The Shift Solenoid A (SSA), Shift Solenoid B (SSB), Shift Solenoid C (SSC) and Shift Solenoid D (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 TCC solenoid is used to control the apply and release of the TCC.
PCM
Various inputs provide information to the PCM to control transmission operation. The PCM then controls outputs which determine transmission operation.