Electronic System Components

Powertrain Control Module (PCM):
Controls operation of the AX4S automatic transaxle. Many input sensors provide information to the powertrain control module. The powertrain control module then controls the actuators which affect transaxle operations.

Air Conditioning Clutch (A/C Clutch): OEM-Factory Installed
The electromagnetic A/C clutch is energized when the A/C cycling 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. The powertrain control module adjusts EPC pressure when the A/C clutch is engaged to compensate for additional load on the engine.

Symptoms:
^ Failed "ON"-EPC pressure slightly low with A/C OFF.
^ Failed "OFF"-EPC pressure slightly high with A/C ON.

Brake Pedal Position (BPP) Switch:
Tells the powertrain control module when the brakes are applied. The switch is closed when the brakes are applied and open when they are released. The BPP switch will also disengage the torque converter clutch when brake is applied.

Symptoms:
^ Failed "ON"-torque converter clutch will not engage at less than one-third throttle.
^ Failed "OFF" or not connected-torque converter clutch will not disengage when brake is applied.

Engine Coolant Temperature (ECT) Sensor:
Detects the temperature of engine coolant and supplies the information to the powertrain control module. The ECT sensor is threaded into 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. On electronic instrument cluster applications, the ECT output is used to control a coolant temperature indicator. The ECT is used to control torque converter clutch operation.

Symptoms: Torque converter clutch will always be off, resulting in reduced fuel economy.

Electronic Ignition(EI) System:
The electronic ignition system consists of the powertrain control module, a crankshaft position sensor and one six-tower ignition coil. The crankshaft position sensor sends a crankshaft position signal to the powertrain control module. The powertrain control module then sends the appropriate ignition signal to the ignition coil. The powertrain control module also uses this signal in the transaxle strategy as well as Wide Open Throttle (WOT) shift control, torque converter clutch control and electronic pressure control.

Symptoms: Harsh engagement and shifts, late WOT shift and no torque converter clutch engagement.

Intake Air Temperature (IAT) Sensor:
Provides the electronic fuel injection system with mixture (fuel and air) temperature information. The intake air temperature sensor is used both to correct density for airflow calculation and to proportion the cold enrichment fuel flow. This sensor is similar in construction to the engine coolant temperature sensor, except it is packaged to improve sensor response time. The sensor is threaded into a cylinder runner of the intake manifold or mounted in the engine air cleaner assembly. The intake air temperature sensor is used in determining EPC pressure.

Symptoms: Incorrect EPC pressure either high or low will result in either harsh or soft shifts.

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 used by the powertrain control module to calculate the injector pulse width for stoichiometry. The powertrain control module also uses this signal for EPC pressure control, shift and torque converter clutch scheduling.

Symptoms: High/low EPC pressure, incorrect shift schedule, incorrect torque converter engagement scheduling and symptoms similar to a throttle position sensor malfunction.

Power Steering Pressure (PSP) Switch:
Is used on certain applications to signal the powertrain control module when the power steering pressure exceeds a specific limit Then the powertrain control module will adjust idle speed to compensate for this added load on the engine. The PSP signal is used as an input to the powertrain control module to assist in determining proper EPC pressure during increased engine loads.

Symptoms:
^ Failed ON-EPC slightly high, firm engagements, firm shifts, harsh coastdown shifts.
^ Failed OFF-EPC pressure slightly low during increased loading of the vehicle power steering.

Throttle Position (TP) Sensor:
Is a potentiometer mounted on the throttle body. The throttle position sensor detects the position of the throttle plate and sends this information to the powertrain control module as a varying voltage signal. If a malfunction occurs in the TP sensor circuit, the powertrain control module will recognize that the TP sensor signal is out of specification The powertrain control module will then operate the AX4S transaxle in a high capacity mode to prevent transaxle damage. The powertrain control module also uses this signal for shift scheduling, EPC pressure control, torque converter clutch control.

Symptoms: Harsh engagements, firm shift feel, abnormal shift schedule, torque converter clutch does not engage, torque converter clutch cycling.

Vehicle Speed Sensor (VSS):
A magnetic pickup that sends a signal to the powertrain control module. The VSS signal tells the powertrain control module the vehicle speed. The PCM uses this signal to control shift scheduling and electronic pressure control.

Symptoms: Harsh engagements, firm shift feel, abnormal shift schedule, unexpected downshifts may occur at closed throttle. Torque converter clutch will not engage.

Transmission Fluid Temperature (TFT) Sensor
The transmission fluid temperature sensor is located on the transaxle main control valve body. It is a temperature-sensitive device called a thermistor. The resistance value of the TFT will vary with transmission fluid temperature change. The powertrain control module monitors the voltage across the TFT to determine the temperature of the transmission fluid. The powertrain control module uses this signal to determine whether a cold start shift schedule is necessary. The cold start shift schedule allows quicker shifts when the transmission fluid is cold. The PCM also inhibits torque converter clutch operation at low transmission fluid temperatures. Corrects EPC pressures for temperature.

Symptoms: Torque converter clutch engagement and stabilized shift schedules happen too soon after a cold start. Harsh or soft shifts.

Digital Transmission Range (DTR) Sensor:
The digital Transmission Range (TR) sensor is located on the outside of the transaxle at the manual lever. The digital TR sensor completes the start circuit in PARK and NEUTRAL and the backup lamp circuit in REVERSE. The TR sensor also opens/closes a set of four switches that are monitored by the Powertrain Control Module (PCM) to determine the position of the manual lever (P, R, N, (D), D, 1).

Symptoms: Engagement concerns, wrong gear, no shifts, increase in EPC pressure.

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

Symptoms: Increased engine rpm on engagements, harsh shifts (converter engaged).

Electronic Pressure Control (EPC) Solenoid:
Regulates transaxle EPC pressure. EPC pressure is used to control line pressure and back out valve function.

Symptoms:
^ Maximum EPC pressure, harsh engagements, harsh shifts.

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

Symptoms:
^ Failed "ON"-engine runs rough/vehicle shudder, engine stalls in DRIVE at low idle speeds (2nd, 3rd, or 4th gear).
^ Failed "OFF"-converter never engages.

Shift Solenoids Assemblies-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 gear selection of 1st through 4th by controlling the pressure of the three shift valves and the forward clutch control valve.

SSA Symptoms: Improper gear selection depending on failure mode and gearshift lever position.
^ Failed ON-3rd gear only.
^ Failed OFF-1st and 2nd gear only.

SSB Symptoms: Improper gear selection depending on failure mode and gearshift lever position.
^ Failed ON-1st and 4th gear only.
^ Failed OFF-2nd and 3rd gear only.

SSC Symptoms: Improper gear selection depending on failure mode and gearshift lever position.
^ Failed ON-No engine braking.
^ Failed OFF-No 4th gear.