Transaxle Electronic Control System

Electronic System Description
The Powertrain Control Module (PCM) and its input/output network controls the following operations:
- shift timing
- fine 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.

Electronic Ignition (EI) System
The electronic ignition system consists of the PCM, a Crankshaft Position Sensor (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 also uses this signal as well as 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 EPC pressure, torque converter clutch operation and shift scheduling.
If a malfunction 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.

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

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 powertrain control module to determine the position of the manual lever (P, R, N, D, 3, 1).

Brake Pedal Position (BPP) Switch
The Brake Pedal Position (BPP) switch tells the powertrain control module 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.

Turbine Shaft Speed (TSS) Sensor
This sensor is a magnetic pickup that sends a signal to the powertrain control module that indicates transaxle turbine shaft input speed. The TSS provides converter turbine speed information for Torque Converter Clutch (TCC) strategy. Also used in determining static EPC pressure settings.

Anti-Lock Brake (ABS) Speed Sensor
The anti-lock brake system uses two sets of variable reluctance speed sensors (two front and two rear) to determine vehicle speed. Four anti-lock sensor indicators (one each wheel) rotate past each wheel speed sensor. The signal generated is proportional to wheel speed and is sent to the anti-lock brake control module. A vehicle speed signal is then broadcast by the anti-lock brake control module on the Standard Corporate Protocol (SCP) Data Link to the powertrain control module as a vehicle speed input signal.

Shift Solenoids (SSA, SSB, SSC)
Three ON/OFF solenoids are used for electronic shift scheduling. The three 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
This sensor is located on the transaxle main control body. It is a temperature-sensitive device called a thermistor. The resistance value of the TFT will vary with temperature change. 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. Corrects EPC pressures for temperature.

Electronic Pressure Control (EPC) Solenoid
This 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.

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

Mass Air Flow (OAF) Sensor
This 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 powertrain control module to calculate the injector pulse width for stoichiometry. 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 Electronic Pressure Control (EPC) pressures.

Air Conditioning 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 is engaged, Electronic Pressure Control (EPC) pressure is adjusted to compensate for the additional load on the engine.

Engine Coolant Temperature (ECT) Sensor
The Engine Coolant Temperature (ECT) sensor detects the temperature of the engine coolant and supplies the information to the powertrain control module. The ECT sensor is used to control Torque Converter Clutch (TCC) operation. The ECT is installed in the heater outlet fitting or cooling passage on the engine. For engine control applications, the ECT signal is used to modify ignition timing, EGR flow and air-to-fuel ratio as a function of engine coolant temperature.