Transmission Electronic Control System
Transmission Electronic Control System
Electronic System Description
The PCM and its input/output network control the following transmission operations:
- Shift timing
- Line pressure (shift feel)
- Torque Converter Clutch (TCC)
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 input signals, 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 hydraulic solenoids to control transmission operation.
The following provides a brief description of each of the sensors and actuators used to control transmission 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 (EPC), shift and TCC scheduling.
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.
Transmission Control Switch (TCS) and Transmission Control Indicator Lamp (TCIL)
The Transmission Control Switch (TCS) is a momentary contact switch. When the switch is pressed, a signal is sent to the PCM to allow automatic shifts from 1st through 4th gears or 1st through 3rd gears only. The PCM energizes the Transmission Control Indicator Lamp (TCIL) when the switch is off. The TCIL indicates overdrive cancel mode activated (lamp on). When the TCIL is flashing, it indicates the EPC circuit shorted or a monitored sensor failure.
Output Shaft Speed (OSS) Sensor
The Output Shaft Speed (OSS) sensor is a magnetic pickup, located at the output shaft ring gear, that sends a signal to the PCM to indicate transmission output shaft speed. The OSS sensor is used for TCC control, shift scheduling and to determine EPC.
Turbine Shaft Speed (TSS) Sensor
The Turbine Shaft Speed (TSS) sensor is a magnetic pickup that sends a signal to the PCM to indicate TSS. The TSS is mounted externally on the case. The PCM uses the TSS signal to help determine appropriate operating pressure and TCC operation.
Transmission Range (TR)
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 (Four-Wheel Drive (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 located in the wire harness near the shift solenoids on the main control valve body. It is a temperature sensitive device called a thermistor. 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 corrects electronic pressure control.
Electronic Pressure Control (EPC) Solenoid
The EPC solenoid regulates transmission pressure. EPC valve pressure is used to control line pressure.
Shift Solenoid A (SSA) and Shift Solenoid B (SSB)
Two on/off shift solenoids provide gear selection of 1st through 4th gears by controlling the pressure to the 3 shift valves. One unit containing the 2 shift solenoids is located in the main control valve body. The shift solenoids are 2-way, normally open solenoids.
a When a manual pull-in occurs above a calibrated speed, the transmission will not downshift from the higher gear until the vehicle speed drops below this calibrated speed.
EC = Electronically Controlled
HD = Hydraulically Disabled
Torque Converter Clutch (TCC) Solenoid
The TCC solenoid is used to control the apply and release of the TCC.
Four-Wheel Drive (4WD) Low (4WDL) Range Switch
The 4WD low (4WDL) 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 shift schedule for 4WDL operation.
Brake Pedal Position (BPP) Switch
The Brake Pedal Position (BPP) switch tells the PCM 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.
Electronic Ignition (EI) System
The Electronic Ignition (EI) system consists of a crankshaft position sensor, two 4-tower 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 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 control and EPC pressure.
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 clutch is engaged, EPC is adjusted by the PCM to compensate for additional load on the engine.
Intake Air Temperature (IAT) Sensor
The Intake Air Temperature (IAT) sensor provides the Sequential Multi-Port Fuel Injection (SFI) system mixture temperature information. The IAT sensor is used both as a density corrector for air flow calculation and to proportion cold enrichment fuel flow. The IAT sensor is installed in the air cleaner inlet tube. The IAT sensor is also used in determining EPC pressures.
Cylinder Head Temperature (CHT) Sensor
The Cylinder Head Temperature (CHT) sensor is a thermistor device in which resistance changes with the temperature. 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 terminals and provides electrical signals to the PCM corresponding to temperature.
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, EPC and TCC control.