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. 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 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 control and electronic pressure control.
Accelerator Pedal Position (APP)
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 (TB). 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), TCC 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.
PCM
The 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.
Transmission Range (TR) Sensor
The Transmission Range (TR) sensor has a 6-pin connector. The TR sensor is located on the inside of the transaxle at the manual lever. The TR sensor sends a signal to the PCM to start the vehicle in PARK and NEUTRAL. The 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 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 sensor provides converter turbine speed information for 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 on the transfer shaft drive gear, that sends a signal to the PCM to indicate transmission output speed. The OSS is used for TCC 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 solenoid and LPC solenoid. The Transmission Fluid Temperature (TFT) 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. Anytime 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 can not 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, SSB, SSC and SSD are Variable Force Solenoid (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 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 TFT is cold to help warm the transmission fluid. The PCM also inhibits TCC operation at low transmission fluid temperatures and adjusts LPC pressures for temperature.
Line Pressure Control (LPC) Solenoid
The LPC solenoid is a 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 reset.
Torque Converter Clutch (TCC) Solenoid
The 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 Electronic Pressure Control (EPC), shift and TCC 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 sensor is used both as a density corrector for airflow calculation and to proportion cold enrichment fuel flow. The IAT sensor is part of the MAF sensor and is installed in the Air Cleaner (ACL) outlet tube. The IAT sensor is also used in determining LPC pressures.
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 if the Electronic Throttle Control (ETC) signal is not available.
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 sensor is used to control TCC operation.