Electronic Control System Components

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.

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 A/C clutch and draws it into engagement with the compressor driveshaft.
When engaged, the A/C clutch is an input to the PCM to adjust EPC pressure for the load on the engine. Also used to adjust Torque Converter Clutch (TCC) modulation when the A/C clutch is engaged.

Symptoms:
^ Failed ON-EPC pressure slightly low with A/C OFF.
^ Failed OFF-EPC pressure slightly high with A/C ON.
^ If erratic A/C operation occurs, the customer may feel improper TCC apply and release.

Brake Pedal Position (BPP) Switch:
The Brake Pedal Position (BPP) switch is connected to the brake pedal. When the brake pedal is pressed, the BPP switch has closed contacts allowing a voltage signal to the PCM.

The PCM releases TCC when the brakes are applied.

Symptoms:
^ Failed "ON"-torque converter clutch will not engage at less than one-third engine throttle.
^ Failed "OFF" or not connected-torque converter clutch will not release 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 automatic transmission applications, the ECT is used to control torque converter clutch solenoid operation. 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.

Symptoms: Torque converter clutch solenoid 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 a 6-tower ignition coil (3.0L). The crankshaft position sensor sends a crankshaft position signal to the Powertrain control module. The PCM then sends the appropriate ignition signal to the ignition coils. The PCM 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.

Ignition Coil-Coil On Plug
The engine uses eight separate coil per plug units. Each coil per plug unit is controlled by the Powertrain Control Module (PCM).

Each coil per plug unit is mounted directly above each spark plug and activates its own spark plug in the proper sequence as controlled by the Powertrain control module.

Intake Air Temperature (IAT) Sensor
Used to determine the EPC pressure. It also provides the electronic fuel injection system with mixture (fuel and air) temperature information. The IAT is used both as a density connector for airflow calculation and to proportion the cold enrichment fuel flow. This sensor is similar in construction to the engine coolant temperature sensor.

Symptoms: Incorrect EPC pressure either high or low resulting 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 PCM to calculate the injector pulse width for stoichiometry. For transaxle strategies, the MAF sensor input is used for EPC pressure control, shift and Torque Converter Clutch (TCC) control.

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. This increase in engine rpm is used as an input to the PCM to adjust EPC pressure to the transaxle.

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

Transmission Control Switch (TCS) and Transmission Control Indicator Lamp (TCIL)
The Transmission Control Switch (TCS) is a momentary contact switch. When this switch is pressed, a signal is sent to the Powertrain control module. The Powertrain control module then energizes the Transmission Control Indicator Lamp (TCIL) and toggles Solenoid 3 SSC, applying the forward clutch to provide engine braking and canceling fourth gear operation.

Sensor: Transmission Control Switch (TCS)
Symptoms: No overdrive cancel when switch is cycled.
Actuator: Transmission Control Indicator Lamp (TCIL)
Transmission Function: Indicates overdrive cancel mode activated (lamp on) and monitored sensor failures (lamp flashing).
Symptoms: Failed "ON"-Overdrive cancel mode always indicated, no flashing for monitored sensor failures. Failed "OFF"-Overdrive cancel mode never indicated, no flashing for monitored sensor failures.

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 powertrain control module as a 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 PCM will recognize that the TP sensor signal is out of specification. The PCM will then operate the AX4N transaxle in a high capacity mode to prevent transaxle damage.

Symptoms: Harsh engagements, firm shift feel, abnormal shift schedule and 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 information to control shift scheduling and EPC pressure.

Symptoms: Harsh engagements, firm shift feel, abnormal shift schedule, unexpected downshifts may occur at closed throttle. Elevated EPC pressures.

Transmission Fluid Temperature (TFT) Sensor
Is located on the transmission main control body. It is a temperature-sensitive device called a thermistor. The resistance value of the TFT will vary with temperature change. The powertrain control module 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.

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 transmission at the manual lever. The digital TR sensor completes the start circuit in Park and Neutral and 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 (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.

Transmission Range (TR) Sensor
The powertrain control module sends a voltage signal to the Transmission Range (TR) sensor. The TR sensor incorporates a series of step-down resistors which act as a voltage divider. The PCM monitors this voltage which corresponds to the position of the manual control lever (P, R, N, D, 2, 1). The TR sensor is located on the outside of the transaxle at the manual control lever. The function of the TR sensor is to determine desired gear and EPC pressure. The TR sensor also contains the park/neutral and backup lamp circuits.

Symptoms: Harsh engagements and firm shift feel. May downshift to a lower near.

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 provides converter turbine speed information for Torque Converter Clutch (TCC) strategy. Also used in determining static EPC pressure settings.

Symptoms: Increased engine rpm on engagements, harsh shifts (converter engaged), delayed shifts with hard apply (slip/bump feel).

Anti-Lock Brake System (ABS) Vehicle Speed Input Signal (SHO Only):
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.

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

Electronic Pressure Control (EPC) 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 transmission 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.

Symptoms:
^ Maximum EPC pressure, harsh encasements, 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-torque converter never engages.

Shift Solenoids Assemblies-SSA, SSB, SSC Switch
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/SS2, and SSC/SS3 provide gear selection of 1st through 4th by controlling the pressure of the three shift valves.

SS1 Symptoms: Improper gear selection depending on failure mode and manual lever position.
^ Failed ON-3rd and 4th gear.
^ Failed OFF-1st and 2nd gear only. SS2 Symptoms: Improper gear selection depending on failure mode and manual control lever position.
^ Failed ON-1st, 3rd and 4th gear only.
^ Failed OFF-2nd and 3rd gear only.
SS3 Symptoms: Improper gear selection depending on failure mode and manual control lever position.
^ Failed ON-No engine braking.
^ Failed OFF-No 4th-gear.