Transaxle Electronic Control System

Transaxle Electronic Control System

Electronic System Description
The powertrain control module (PCM) and its input/output network control the following operations:
^ Shift timing
^ Line pressure (shift feel)
^ Torque converter clutch

The transaxle 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 transaxle 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 transaxle-related sensors and switches. The PCM also uses these signals when determining transaxle 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 torque converter clutch. It will also determine the best line pressure needed to optimize shift feel. To accomplish this the PCM uses output solenoids to control transaxle operation.

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

Powertrain Control Module (PCM)
The powertrain control module (PCM) controls operation of the transaxle. Many input sensors provide information to the PCM. The PCM then controls the actuators which affect transaxle operation.

Electronic Ignition (EI) System
The electronic ignition (EI) system consists of the PCM, a crankshaft position (CKP) sensor and two 4-tower ignition coils. The crankshaft position sensor sends a crankshaft position signal to the PCM. The PCM then sends the appropriate ignition signal to the ignition coils. The PCM uses this signal and wide open throttle (WOT) shift control, torque converter clutch control and electronic pressure control.

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 processor assembly as varying voltage signal.

The PCM uses the monitored voltage level of the TP sensor for control of electronic pressure control (EPC) pressure, torque converter clutch operation and shift scheduling.

If a failure occurs in the TP sensor circuit, the processor will recognize that the TP sensor signal is out of specification, The processor will then operate the transaxle in a high capacity mode to prevent transaxle damage.

Brake Pedal Position (BPP) Switch
The brake pedal position (BPP) switch tells the PCM when the brakes are applied. The torque converter clutch disengages when the brakes are applied. The BPP switch closes when the brakes are applied and opens when they are released.

Digital Transmission Range (TR) Sensor
The digital transmission range (TR) sensor has a twelve-pin connector. The sensor is located on the outside of the transaxle at the manual lever. The digital sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE. The digital TR sensor also opens/closes a set of four switches that are monitored by the PCM to determine the position of the manual lever (P, R, N, (D) , D, 1).





Check Transaxle Light
The Check Transaxle Light will flash when the transaxle has overheated 149°C (300°F). Other transaxle faults will also cause the Check Transaxle Light to flash. Currently, the KOEO bulb function test is not available on this powertrain control module (PCM) output. Diagnostic test-out may be completed for this PCM output by using the scan tool or WDS tester. The PIDs are:
^ TCILF = NO (OK)
^ TCILF = YES (BAD)

Turbine Shaft Speed (TSS) Sensor
This turbine shaft speed (TSS) sensor is a magnetic pickup that sends a signal to the PCM that indicates transaxle turbine shaft input speed. The TSS provides converter turbine speed information for torque converter clutch (TCC) strategy. It is also used in determining static EPC pressure settings.

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 is used for torque converter clutch control, speed scheduling and to determine electronic pressure control.

Shift Solenoids (SSA, SSB, SSC)
Three ON/OFF solenoids are used for electronic shift scheduling. The solenoids are located in the main control valve body. The solenoids are two-way, normally open style. Solenoids SSA, SSB, and SSC provide selection of first through fourth gear by controlling the pressure of the three shift valves.

Transmission Fluid Temperature (TFT) Sensor
The transmission fluid temperature (TFT) sensor is located on the transaxle main control body. It has a temperature sensitive device called a thermistor. The resistance value of the TFT will vary with temperature fluctuation. The PCM monitors the voltage across the TFT to determine the temperature of the transmission fluid.

The PCM uses this initial signal to determine whether a cold start shift schedule is necessary. The cold start shift schedule allows quicker shifts when the transmission fluid temperature is cold. The PCM also inhibits torque converter clutch operation at low transmission fluid temperatures. The TFT sensor corrects EPC pressure for different fluid temperatures.

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. It supplies EPC which regulates transaxle line pressure and line modulator pressure. This is done by producing resisting forces to the main regulator and line modulator circuits. These two pressures control clutch application pressures.

The PCM has an adaptive learn strategy to electronically control the transaxle which will automatically adjust the shift feel. The first few hundred miles of operation of the transaxle may have abrupt shifting. This is a normal operation. If the battery has been disconnected for any reason it will need to be kept disconnected for approximately 20 minutes to reset the adaptive shift pressure strategy or use the scan tool to do the keep alive memory (KAM) reset.

Torque Converter Clutch (TCC) Solenoid
The torque converter clutch (TCC) solenoid is used in the transaxle control system to control the application, modulation and release of the torque converter clutch.

Mass Air Flow (MAF) Sensor
The mass air flow (MAF) sensor directly measures the mass of the air flowing into the engine. The sensor output is a DC (analog) signal ranging from about 0.5 volt to 5.0 volts by the PCM to calculate the injector pulse width for the correct air fuel combustion ratio. The MAF sensor input is used for EPC pressure control, shift and torque converter clutch (TCC) control.

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 air flow 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 EPC pressures.