Transmission Electronic Control System
Transmission Electronic Control System
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 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 input information from certain engine-related and driver-demand related sensors and switches.
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.
PCM
Various inputs provide information to the PCM to control transmission operation. The PCM then controls outputs which determine transmission operation.
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 clutch is engaged, Electronic Pressure Control (EPC) solenoid control is adjusted by the PCM to compensate for additional engine load.
Brake Pedal Position (BPP) Switch
The Brake Pedal Position (BPP) sends a signal to the PCM indicating when the brakes are applied. The TCC will disengage when the brakes are applied. The BPP switch closes when the brake pedal is applied and opens when released.
Cylinder Head Temperature (CHT) Sensor
The Cylinder Head Temperature (CHT) 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.
Ignition Coil - Coil-On-Plug
The engine uses 8 separate coil-on-plug units. Each coil-on-plug unit is controlled by the PCM.
Each coil-on-plug unit is mounted directly above each spark plug and activates its own spark plug in the correct sequence as controlled by the PCM.
Refer to Computers and Control Systems Information for additional information on the ignition system.
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 EPC valve pressure which is used to control line pressure. The IAT sensor is part of the Mass Air Flow (MAF) sensor.
Mass Air Flow (MAF) Sensor
The 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.
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 (O/D) cancel mode activated (lamp on). When the TCIL is flashing, it indicates an EPC circuit shorted or a monitored sensor failure.
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 solenoid control and TCC scheduling.
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, and the back-up lamp circuit in REVERSE. The TR sensor also opens/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).
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 rpm. The OSS sensor is used for TCC scheduling, 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 transmission turbine shaft rpm. The TSS is mounted externally on the case. The PCM uses the TSS signal to determine appropriate operating pressure and TCC scheduling.
Electronic Pressure Control (EPC) Solenoid
The Electronic Pressure Control (EPC) solenoid regulates transmission pressure. The EPC valve position is used to control line pressure.
Torque Converter Clutch (TCC) Solenoid
The Torque Converter Clutch (TCC) solenoid is used to control the apply and release of the torque converter.
Shift Solenoid - Shift Solenoid A (SSA), 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 valves.
Solenoid Operation Chart
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
Transmission Fluid Temperature (TFT) Sensor
The Transmission Fluid Temperature (TFT) sensor is located on the transmission harness near the shift solenoids on the main control valve body. It is a temperature-sensitive thermistor. It sends a voltage signal to the PCM. The voltage signal varies with TFT. The PCM uses this signal to determine whether a cold start shift schedule is necessary. The shift schedule is compensated when the TFT is cold. The PCM also inhibits TCC operation at low TFT and selects the correct EPC.