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 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 transmission-related sensors and switches. The PCM also uses these inputs 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. The PCM 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

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.


A/C Clutch

An electromagnetic clutch is energized when the A/C cycling pressure switch closes. The switch is located on the suction side of the 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, the Electronic Pressure Control (EPC) solenoid is adjusted by the PCM to compensate for additional engine load.


Brake Pedal Position (BPP) Switch

The Brake Pedal Position (BPP) switch sends a voltage input to the Lighting Control Module (LCM) which then sends a network signal to the PCM that the brakes are applied. If engaged, the TCC disengages when the brakes are applied. The BPP switch closes when the brakes are applied and opens when they are released.


Cylinder Head Temperature (CHT) Sensor

The Cylinder Head Temperature (CHT) sensor is a thermistor device in which resistance changes with the temperature. The resistance of the 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 an electrical input to the PCM corresponding to temperature.


Electronic Pressure Control (EPC) Solenoid

The EPC solenoid regulates transmission pressure. EPC valve pressure is used to control line pressure.


Ignition Coil - Coil On Plug

The engine uses 8 separate coil per plug units. Each coil per plug unit is controlled by the PCM.

Each coil per 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 for 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 air temperature. The IAT sensor is installed in the Air Cleaner (ACL) outlet tube. The IAT sensor is used in determining EPC valve pressure which is used to control line pressure.


Mass Air Flow (MAF) Sensor

The Mass Air Flow (MAF) sensor measures the speed and density of air flowing into the intake manifold. For transmission strategies, the MAF sensor is used to regulate EPC, shift time 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 the EPC or 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 a voltage input to the PCM. The TP sensor is used for shift time, EPC valve pressure 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 control 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 OSS. The OSS sensor is used for TCC scheduling, shift time and to determine EPC valve pressure.


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 scheduling.


Torque Converter Clutch (TCC) Solenoid

The TCC solenoid is used to control the apply and release of the TCC.


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


Transmission Fluid Temperature (TFT) Sensor

The Transmission Fluid Temperature (TFT) sensor is connected to the transmission wire harness and is located 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 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 s and adjusts EPC valve pressure.