Powertrain Control Module

AUTOMATIC SHUTDOWN (ASD) RELAY SENSE - PCM INPUT
The ASD relay is located in the Power Distribution Center (PDC). The PDC is located in the engine compartment. Refer to label on PDC cover for relay location.

A 12 volt signal at this input indicates to the PCM that the ASD has been activated. The relay is used to connect the oxygen sensor heater element, ignition coil and fuel injectors to a 12 volt power supply.

This input is used only to sense that the ASD relay is energized. If the Powertrain Control Module (PCM) does not see 12 volts at this input when the ASD should be activated, it will set a Diagnostic Trouble Code (DTC).

BATTERY VOLTAGE - PCM INPUT
The battery voltage input provides power to the Powertrain Control Module (PCM).

BRAKE SWITCH - PCM INPUT
When the brake light switch is activated, the Powertrain Control Module (PCM) receives an input indicating that the brakes are being applied. After receiving this input, the PCM disables vent and vacuum solenoid output signals to the speed control servo.

CCD BUS (+/-) CIRCUITS - ECM/PCM INPUTS AND OUTPUTS
The Engine Control Module (ECM) and the Powertrain Control Module (PCM) send certain signals through the CCD bus circuits. Some of these signals are parallel circuited between the two control modules (ECM and PCM). These signals are used to control certain instrument panel located items and to determine certain identification numbers.

FUEL LEVEL SENSOR - PCM INPUT
The fuel level sensor (fuel gauge sending unit) is located on the fuel tank module.

Refer to Fuel Gauge Sending Unit in Fuel Delivery for more information.

IGNITION CIRCUIT SENSE - PCM INPUT
This circuit ties the ignition switch to the Powertrain Control Module (PCM).

The ignition circuit sense input tells the PCM the ignition switch has energized the ignition circuit.

Battery voltage is also supplied to the PCM through the ignition switch when the ignition is in the RUN or START position. This is referred to as the "ignition sense" circuit and is used to "wake up" the PCM. Voltage on the ignition input can be as low as 6 volts and the PCM will still function. Voltage is supplied to this circuit to power the PCM's 8 volt regulator. The battery voltage on this line is supplied to the 8 volt regulator, which then passes on a power-up supply to the 5 volt regulator.

POWER GROUNDS
The Powertrain Control Module (PCM) has 2 main grounds. Both of these grounds are referred to as power grounds. All of the high-current, noisy, electrical devices are connected to these grounds as well as all of the sensor returns. The sensor return comes into the sensor return circuit, passes through noise suppression, and is then connected to the power ground.

The power ground is used to control ground circuits for the following PCM loads:
- Generator field winding
- Certain relays/solenoids
- Certain sensors

SENSOR RETURN - PCM INPUT
The Sensor Return circuits are internal to the Powertrain Control Module (PCM).

Sensor Return provides a low-noise ground reference for all engine control system sensors. Refer to Power Grounds for more information.

SIGNAL GROUND - PCM INPUT
Signal ground provides a low noise ground to the data link connector.

VEHICLE SPEED AND DISTANCE - PCM INPUT
Vehicle speed and distance covered are measured by the Rear Wheel Speed Sensor. The sensor is mounted to the rear axle. A signal is sent from this sensor to the Controller Antilock Brake (CAB) computer. A signal is then sent from the CAB to the Powertrain Control Module (PCM) to determine vehicle speed and distance covered. The PCM will then determine strategies for fuel system and speed control system operation.

AUTO SHUTDOWN (ASD) RELAY - PCM OUTPUT
The 5-pin, 12 volt, Automatic Shutdown (ASD) relay is located in the Power Distribution Center (PDC). Refer to label on PDC cover for relay location.

The ASD relay supplies battery voltage (12+ volts) to the fuel injectors and ignition coil(s). With certain emissions packages it also supplies 12-volts to the oxygen sensor heating elements.

The ground circuit for the coil within the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM operates the ASD relay by switching its ground circuit ON and OFF.

The ASD relay will be shutdown, meaning the 12 volt power supply to the ASD relay will be de-activated by the PCM if:
- the ignition key is left in the ON position. This is if the engine has not been running for approximately 1.8 seconds.
- there is a crankshaft position sensor signal to the PCM that is lower than pre-determined values.

The PCM will sense if or when the ASD relay has been activated through a "sense circuit". Refer to Automatic Shutdown (ASD) Relay Sense - PCM Input for additional information.

DATA LINK CONNECTOR - PCM INPUT AND OUTPUT
The data link connector is located at the lower edge of the instrument panel near the steering column.

The 16-way data link connector (diagnostic scan tool connector) links the Diagnostic Readout Box (DRB) scan tool or the Mopar Diagnostic System (MDS) with the Powertrain Control Module (PCM).