Power Distribution Module: Description and Operation

Fig.2 Battery Thermal Guard:

INTEGRATED POWER MODULE
The Integrated Power Module (IPM) is a combination of the Power Distribution Center (PDC) and the Front Control Module (FCM). The IPM is located in the engine compartment, next to the battery on this model (Fig. 2). The power distribution center mates directly with the Front Control Module (FCM) to form the IPM Fuse and Relay Center. The power distribution center (PDC) is a printed circuit board based module that contains fuses and relays, while the front control module contains the electronics controlling the IPM and other functions. This IPM connects directly to the battery positive via a four pin connector. The ground connection is via two other connectors. The IPM provides the primary means of voltage distribution and protection for the entire vehicle.

The molded plastic IPM housing includes a base and cover. The IPM cover is easily opened or removed for service access by squeezing the two marked cover latches and has a fuse and relay layout map integral to the inside surface of the cover. This IPM housing base and cover are secured in place by an IPM mounting bracket. This mounting bracket is designed to allow the IPM to rotate counter-clockwise once the locking tab is disengaged. The IPM mounting bracket is secured in place by bolts threaded into the left front wheel house.

Replaceable components of the IPM assembly are broken down into the following components: the Power Distribution Center (PDC) (without fuses or relays), the IPM cover, the Front Control Module (FCM), the IPM mounting bracket, IPM bracket retaining clips and the IPM assembly which includes the power distribution center, the cover and FCM.

Refer to the Front Control Module in the Electronic Control Module for information on the FCM.

All of the current from the battery and the generator output enters the Integrated Power Module (IPM) via a four-pin connector on the bottom of the module. The IPM cover is unlatched and opened or removed to access the fuses or relays. Internal connections of all of the power distribution center circuits is accomplished by a combination of bus bars and a printed circuit board. Refer to the Wiring for complete IPM circuit schematics.

Fig.11 Powertrain Control Module (PCM):

POWERTRAIN CONTROL MODULE
The Powertrain Control Module (PCM) is a digital computer containing a microprocessor (Fig. 11). The PCM receives input signals from various switches and sensors referred to as Powertrain Control Module Inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices referred to as Powertrain Control Module Outputs.

NOTE: PCM Inputs:
- Air Conditioning Pressure Transducer
- ASD Relay
- Battery Voltage
- Brake Switch
- Camshaft Position Sensor
- Crankshaft Position Sensor
- Distance Sensor (from transmission control module)
- EGR Position Feedback
- Engine Coolant Temperature Sensor Heated Oxygen Sensors
- Ignition sensor
- Intake Air Temperature Sensor
- Knock Sensor
- Leak Detection Pump Feedback
- Manifold Absolute Pressure (MAP) Sensor
- Park/Neutral (from transmission control module)
- PCI Bus
- Power Steering Pressure Switch
- Proportional Purge Sense
- SCI Receive
- Speed Control
- Throttle Position Sensor
- Torque Management Input (From TCM)
- Transaxle Control Module (TCM)
- Transaxle Gear Engagement (From TCM)
- Vehicle Speed (from transmission control module)

NOTE: PCM Outputs:
- Air Conditioning Clutch Relay
- Automatic Shut Down (ASD) and Fuel Pump Relays
- Data Link Connector (PCI and SCI Transmit)
- Double Start Override
- EGR Solenoid
- Fuel Injectors
- Generator Field
- High Speed Fan Relay
- Idle Air Control Motor
- Ignition Coils
- Leak Detection Pump
- Low Speed Fan Relay
- MTV Actuator
- Proportional Purge Solenoid
- SRV Valve
- Speed Control Relay
- Speed Control Vent Relay
- Speed Control Vacuum Relay
- 8 Volt Output
- 5 Volt Output

Based on inputs it receives, the powertrain control module (PCM) adjusts fuel injector pulse width, idle speed, ignition timing, and canister purge operation. The PCM regulates the cooling fans, air conditioning and speed control systems. The PCM changes generator charge rate by adjusting the generator field.

The PCM adjusts injector pulse width (air-fuel ratio) based on the following inputs.
- Battery Voltage
- Intake Air Temperature Sensor
- Engine Coolant Temperature
- Engine Speed (crankshaft position sensor)
- Exhaust Gas Oxygen Content (heated oxygen sensors)
- Manifold Absolute Pressure
- Throttle Position

The PCM adjusts engine idle speed through the idle air control motor based on the following inputs.
- Brake Switch
- Engine Coolant Temperature
- Engine Speed (crankshaft position sensor)
- Park/Neutral (transmission gear selection)
- Transaxle Gear Engagement
- Throttle Position
- Vehicle Speed (from Transmission Control Module)

The PCM adjusts ignition timing based on the following inputs.
- Intake Air Temperature
- Engine Coolant Temperature
- Engine Speed (crankshaft position sensor)
- Knock Sensor
- Manifold Absolute Pressure
- Park/Neutral (transmission gear selection)
- Transaxle Gear Engagement
- Throttle Position

The automatic shut down (ASD) and fuel pump relays are mounted externally but turned ON and OFF by the powertrain control module through the same circuit.

The camshaft and crankshaft signals are sent to the powertrain control module. If the PCM does not receive both signals within approximately one second of engine cranking, it deactivates the ASD and fuel pump relays. When these relays are deactivated, power is shut OFF to the fuel injectors, ignition coils, fuel pump and the heating element in each oxygen sensor.

The PCM contains a voltage converter that changes battery voltage to a regulated 8.0 volts. The 8.0 volts power the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5.0 volts supply for the engine coolant temperature sensor, intake air temperature sensor, manifold absolute pressure sensor and throttle position sensor.

The PCM engine control strategy prevents reduced idle speeds until after the engine operates for 320 km (200 miles). If the PCM is replaced after 320 km (200 miles) of usage, update the mileage in new PCM. Use the DRB scan tool to change the mileage in the PCM. Refer to the appropriate Powertrain Diagnostic Manual and the DRB scan tool.

FRONT CONTROL MODULE
The Front Control Module (FCM) is a micro-controller based module located in the engine compartment. This FCM mates to the Power Distribution Center (PDC) to form the Integrated Power Module (IPM). The IPM connects directly to the battery and provides the primary means of circuit protection and power distribution for all vehicle electrical systems. The FCM controls power to some of these vehicle systems electrical and electromechanical loads based on inputs received from hard wired switch inputs and data received on the Programmable Communications Interface (PCI) data bus.

As messages are sent over the Programmable Communications Interface (PCI) data bus, the Front Control Module (FCM) reads these messages and controls power to some of the vehicles electrical systems by completing the circuit to ground (low side driver) or completing the circuit to 12 volt power (high side driver).

The following functions are controlled by the Front Control Module:
- Accessory Relay Actuation
- Brake Transmission Shift Interlock Functions (BTSI)
- Diesel Cabin Heater (Diesel Engine Vehicles)
- Electronic Back Light (EBL) Rear Defogger
- Electronic Transaxle (Gasoline engine Vehicles)
- Front and Rear Blower Motor Relay Actuation
- Front Fog Lamp Relay Actuation
- Front Washer Motor
- Front Windshield Wiper "HI" & "LO" Relay Actuation
- Front Windshield Wiper "ON" Relay Actuation
- Headlamp Power with Voltage Regulation
- Horn Relay Actuation
- Headlamp Washer Relay Actuation
- Name Brand Speaker (NBS) Relay Actuation
- Occupant Restraint Controller Voltage
- Park Lamp Relay Actuation
- Rear Washer Motor
- Side Airbag Voltage

The following inputs are Received/Monitored by the Front Control Module:
- Ambient Temperature Sensing
- Back-Up switch
- Brake Fluid Level
- B+ Connection Detection
- Engine Crank Signal (Diesel Engine Vehicles)
- Horn Input
- Ignition Switch Start Only
- Ignition Switch Run and Start Only
- Stop Lamp Sense
- Washer Fluid Level
- Windshield Wiper Park