Transaxle Electronic Control System

Transaxle Electronic Control System

Electronic System Description

The PCM and its input/output network controls the following operations:

- Shift timing

- Line pressure (shift feel)

- Torque Converter Clutch (TCC)

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 TCC (Torque Converter Clutch). It will also determine the best line pressure needed to optimize shift engagement 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)

The Electronic Ignition (EI) system consists of the PCM, a Crankshaft Position (CKP) sensor and ignition coils. The CKP (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, TCC (Torque Converter Clutch) control and electronic pressure control.

Accelerator Pedal Position (APP)

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal. The APP (Accelerator Pedal Position) detects the position of the accelerator pedal and inputs this information as a voltage to the PCM. The PCM uses APP (Accelerator Pedal Position) sensor information to aid in determining line pressure, shift scheduling and TCC (Torque Converter Clutch) operation. Failure of this sensor will cause the transmission to operate at higher line pressure to avoid damage to the transmission. This higher line pressure causes harsh upshifts and harsh engagements.

Throttle Position (TP) Sensor

The Throttle Position (TP) sensor is a potentiometer mounted on the Throttle Body (TB). The TP (Throttle Position) 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 (Throttle Position) sensor for control of Line Pressure Control (LPC), TCC (Torque Converter Clutch) operation and shift scheduling.

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

PCM

The PCM controls operation of the transaxle. Many input sensors provide information to the PCM. The PCM then controls the actuators which affect transaxle operation.

Transmission Range (TR) Sensor

The Transmission Range (TR) sensor has a 6-pin connector. The TR (Transmission Range) sensor is located on the inside of the transaxle at the manual lever. The TR (Transmission Range) sensor sends a signal to the PCM to start the vehicle in PARK and NEUTRAL. The TR (Transmission Range) sensor 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, L).

Brake Pedal Position (BPP) Switch

The Brake Pedal Position (BPP) switch tells the PCM when the brakes are applied. The BPP (Brake Pedal Position) switch closes when the brakes are applied and opens when they are released. The BPP (Brake Pedal Position) signal is used for brake shift interlock actuation.

Turbine Shaft Speed (TSS) Sensor

This Turbine Shaft Speed (TSS) sensor is a Hall-effect pickup that sends a signal to the PCM that indicates transaxle turbine shaft input speed. The TSS (Turbine Shaft Speed) sensor provides converter turbine speed information for TCC (Torque Converter Clutch) strategy. Also used in determining static LPC (Line Pressure Control) pressure settings.

Output Shaft Speed (OSS) Sensor

The Output Shaft Speed (OSS) sensor is a Hall-effect pickup, located on the transfer shaft drive gear, that sends a signal to the PCM to indicate transmission output speed. The OSS (Output Shaft Speed) is used for TCC (Torque Converter Clutch) control and shift scheduling.

Solenoid Body

NOTICE: If the solenoid body identification and strategy does not match the solenoid body information in the Powertrain Control Module (PCM), transaxle damage or driveability concerns can occur.

The solenoid body contains 7 solenoids, 5 shift solenoids (Shift Solenoid A (SSA), Shift Solenoid B (SSB), Shift Solenoid C (SSC), Shift Solenoid D (SSD) and Shift Solenoid E (SSE)), TCC (Torque Converter Clutch) solenoid and LPC (Line Pressure Control) solenoid. The Transmission Fluid Temperature (TFT) sensor is also located in the solenoid body. The solenoid body is serviced as an assembly.

The solenoid body has a unique strategy data file that must be downloaded to the PCM. There is a 7-digit solenoid body identification and a 13-digit solenoid body strategy for each solenoid body. Any time a new solenoid body is installed or the transaxle is installed, the scan tool must be used to get the solenoid body strategy data file and download it into the PCM.

If the PCM is replaced and the PCM data cannot be inhaled or exhaled, the solenoid body identification and solenoid body strategy must be downloaded into the PCM.

Shift Solenoid A (SSA), Shift Solenoid B (SSB), Shift Solenoid C (SSC), Shift Solenoid D (SSD) and Shift Solenoid E (SSE)

Five shift solenoids are used for electronic shift scheduling. The 5 solenoids are located in the solenoid body. SSA (Shift Solenoid A), SSB (Shift Solenoid B), SSC (Shift Solenoid C) and SSD (Shift Solenoid D) are Variable Force Solenoid (VFS). SSE (Shift Solenoid E) is an ON/OFF shift solenoid. Shift solenoids SSA (Shift Solenoid A), SSB (Shift Solenoid B), SSC (Shift Solenoid C), SSD (Shift Solenoid D) and SSE (Shift Solenoid E) provide selection of 1st through 6th gears and reverse by controlling the pressure of the shift valves. SSA (Shift Solenoid A) and SSC (Shift Solenoid C) are normally low-pressure solenoids. Pressure increases as the PCM activates the solenoid. SSB (Shift Solenoid B) and SSD (Shift Solenoid D) are normally high-pressure solenoids. Pressure decreases as the PCM activates the solenoid. SSE (Shift Solenoid E) is normally closed and opens when the PCM activates the solenoid. The solenoids are activated by the PCM controlling current flow at the solenoid ground circuit, this is known as ground side switching.

Transmission Fluid Temperature (TFT) Sensor

This sensor is located in the transaxle solenoid body. It is a temperature-sensitive device called a thermistor. The resistance value of the TFT (Transmission Fluid Temperature) sensor will vary with temperature change. The PCM monitors the voltage across the TFT (Transmission Fluid Temperature) sensor 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 delayed shifts when the transmission fluid is cold to help warm the transmission fluid. The PCM also inhibits TCC (Torque Converter Clutch) operation at low transmission fluid temperatures and adjusts LPC (Line Pressure Control) pressures for temperature.

Line Pressure Control (LPC) Solenoid

The LPC (Line Pressure Control) solenoid is a VFS (Variable Force Solenoid). The VFS (Variable Force Solenoid) is an electro-hydraulic actuator combining a solenoid and a regulating valve. It supplies the pressure which regulates transaxle line pressure. This is done by producing resisting forces to the main regulator and line modulator circuits. These 2 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. The battery will need to be kept disconnected for approximately 20 minutes, if it has been disconnected, 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 TCC (Torque Converter Clutch) 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

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 volts by the PCM to calculate the injector pulse width for stoichiometry. The Mass Air Flow (MAF) sensor input is used for Electronic Pressure Control (EPC), shift and TCC (Torque Converter Clutch) control.

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 (Intake Air Temperature) sensor is used both as a density corrector for airflow calculation and to proportion cold enrichment fuel flow. The IAT (Intake Air Temperature) sensor is part of the MAF (Mass Air Flow) sensor and is installed in the Air Cleaner (ACL) outlet tube. The IAT (Intake Air Temperature) sensor is also used in determining LPC (Line Pressure Control) 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. The CHT (Cylinder Head Temperature) sensor is used to control TCC (Torque Converter Clutch) operation.