Transaxle Electronic Control System

Transaxle Electronic Control System

Electronic System Description
The powertrain control module (PCM) and its input/output network controls these 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 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.

This is a brief description of each of the sensors and actuators used to control transaxle operation.

Electronic Ignition (EI) System
The electronic ignition (EI) system consists of the PCM, a crankshaft position (CKP) sensor and 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.

Accelerator Pedal Position (APP) Sensor
The accelerator pedal position (APP) sensor is mounted on the accelerator pedal. The APP detects the position of the accelerator pedal and inputs this information as a voltage to the PCM. The PCM uses APP sensor information to aid in determining line pressure, shift scheduling and TCC 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. 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 line pressure control (LPC), 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 (PCM) controls operation of the transaxle. Many input sensors provide information to the powertrain control module. The PCM then controls the actuators which affect transaxle operation.

Digital Transmission Range (TR) Sensor
The digital transmission range (TR) sensor has a 6-pin connector. The sensor is located on the inside of the transaxle at the manual lever. The digital TR sensor sends a signal to the PCM to start the vehicle in PARK and NEUTRAL. The digital TR 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 switch closes when the brakes are applied and opens when they are released. The BPP signal is used for brake shift interlock actuation.

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

Output Shaft Speed (OSS) Sensor
The output shaft speed (OSS) sensor is a hall effect pickup, located at the output shaft ring gear, that sends a signal to the powertrain control module to indicate transmission output speed. The OSS is used for torque converter clutch control and shift scheduling.

Solenoid Body
The solenoid body contains 7 solenoids. 5 shift solenoids (SSA, SSB, SSC, SSD and SSE), torque converter clutch (TCC) solenoid and line pressure control (LPC) solenoid. The transmission fluid temperature (TFT) is also located in the solenoid body. The solenoid body is serviced as an assembly.

CAUTION: If the solenoid body ID and strategy does not match the solenoid body information in the PCM, transaxle damage or driveability concerns can occur.

The solenoid body has a unique strategy data file that must be downloaded to the PCM. there is a 7-digit solenoid body ID and a 13-digit solenoid body strategy for each solenoid body. Anytime a new solenoid body is installed or the transaxle is installed, the scan tool (PDS or IDS) 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 can not be inhaled or exhaled, the solenoid body ID and solenoid body strategy must be downloaded into the PCM.

Shift Solenoids (SSA, SSB, SSC, SSD, SSE)
Five solenoids are used for electronic shift scheduling. The 5 solenoids are located in the solenoid body. SSA, SSB, SSC and SSD are variable force solenoids (VFS). SSE is an ON/OFF shift solenoid. Shift solenoids SSA, SSB, SSC, SSD and SSE provide selection of 1st through 6th gears and reverse by controlling the pressure of the shift valves. SSA and SSC are normally low pressure solenoids. Pressure increases as the PCM activates the solenoid. SSB and SSD are normally high pressure solenoids. Pressure decreases as the PCM activates the solenoid. SSE 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 transmission fluid temperature (TFT) sensor 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 delayed shifts when the transmission fluid temperature is cold to help warm the transmission fluid. The PCM also inhibits torque converter clutch operation at low transmission fluid temperatures and adjusts LPC pressures for temperature.

Line Pressure Control (LPC) Solenoid
The line pressure control (LPC) 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 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. 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
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 EPC pressure control, shift and 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 line pressure control (LPC) 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 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.