General System Description

Introduction
All engines use in this section have a sequential Multi-Port Electronic Fuel Injection system. The MPI system is computer regulated and provides precise (air) fuel ratios for all driving conditions. The Powertrain Control Module (PCM) operates the fuel injection system.

The PCM regulates:
- Ignition timing
- Air/fuel ratio
- Emission control devices
- Cooling fan
- Charging system
- Idle speed
- Vehicle speed control

Various sensors provide the inputs necessary for the PCM to correctly operate these systems. In addition to the sensors, various switches also provide inputs to the PCM.

All inputs to the PCM are converted into signals. The PCM can adapt its programming to meet changing operating conditions.

Fuel is connected into the intake port above the intake valve in precise metered amounts through electrically operated injectors. The PCM fires the injectors in a specific sequence. Under most operating conditions, the PCM maintains an air fuel ratio of 14.7 parts air to 1 part fuel by constantly adjusting injector pulse width. Injector pulse width is the length of time the injector is open.

The PCM adjusts injector pulse width by opening and closing the ground path to the injector. Engine RPM (speed) and manifold absolute pressure (air density) are the primary inputs that determine injector pulse width

System Diagnosis
The PCM can test many of its own input and out-put circuits. If the PCM senses a fault in a major system, the PCM stores a Diagnostic Trouble Code (DTC) in memory

Fig. 1 Power Distribution Center (PDC):

Power Distribution Center
The power distribution center (PDC) is located next to the battery (Fig. 1). The PDC contains the starter relay, radiator fan relay, A/C compressor clutch relay. auto shutdown relay, fuel pump relay and several fuses.

CCD BUS
Various modules exchange information through a communications port called the CCD Bus. The powertrain control module (PCM) transmits the Malfunction Indicator Lamp (Check Engine) On/Off signal and engine RPM on the CCD Bus. The PCM receives the Air Conditioning elect input, transaxle gear position input and speed control engage inputs over the CCD Bus. The PCM also receives the air conditioning evaporator temperature signal from the CCD Bus.

The following components access or send information on the CCD Bus.
- Instrument Panel
- Body Control Module
- Air Bag System Diagnostic Module
- Full A/C Display Head
- ABS Module
- Transmission Control Module
- Powertrain Control Module
- Overhead Travel Module

Fig. 2 Powertrain Control Module (PCM):

Powertrain Control Module
The powertrain control module (PCM) is a digital computer containing a microprocessor (Fig. 2). 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.

PCM Inputs:
- Air Conditioning Pressure Transducer
- Battery Voltage
- Brake Switch
- Camshaft Position Sensor
- CCD Bus
- Crankshaft Position Sensor
- Intake Air Temperature Sensor (3.3L Only)
- Distance Sensor (from transmission control module)
- Transaxle Control Module (TCM)
- Transaxle Gear Engagement (From TCM)
- Torque Management Input (From TCM)
- Engine Coolant Temperature Sensor
- Knock Sensor (3.5L Engine only)
- Manifold Absolute Pressure (MAP) Sensor
- Heated Oxygen Sensors
- Ignition sense
- Park/Neutral (from transmission control module)
- SCI Receive
- Speed Control
- Throttle Position Sensor
- Vehicle Speed (from transmission control module)

PCM Outputs:
- Air Conditioning Clutch Relay
- Automatic Shut Down (ASD) and fuel Pump Relay
- Data Link Connector CCD and SCI Transmit
- Duty Cycle EVAP Purge Solenoid
- EGR Solenoid
- Fuel Injectors
- Generator Field
- High Speed Fan Relay
- Idle Air Control Motor
- Ignition Coils
- Low Speed Fan Relay
- MTV Solenoid
- Speed Control Relay
- Speed Control Vent Relay
- Speed Control Vacuum Relay

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 charges 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 (3.3L Only)
- 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 (3.3L Only)
- Engine Cool and 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 5.0 volts. The 5.0 volts power the camshaft position sensor. crank-shaft 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 iii the PCM.