Computers and Control Systems: Description and Operation

GENERAL DESCRIPTION

Computer Network:

This vehicle uses several electronic components which form an electronic computer network, designed to control various engine and body sub-systems. The heart of the computer network is the Body Computer Module (BCM). The BCM has an internal microprocessor which is the center for communication with all the other components, and controls the on-board diagnostics of the vehicle. All system sensors and switches are monitored by the BCM or one of the five other major components that complete the computer system network. The other five components are the Diagnostic Energy Reserve Module (DERM) (Supplemental Inflatable Restraint (SIR) controller), Electronic Climate Control (ECC) panel, Heating, Ventilation, and Air Conditioning (HVAC) programmer, the Instrument Panel Cluster (IPC), and the Powertrain Control Module (PCM).

DIAGNOSTIC ENERGY RESERVE MODULE (SIR CONTROLLER)
The DERM monitors, detects, and records the SIR system during operation when system components malfunction, stores the malfunction as a trouble code, and maintains a 36.0 volt loop reserve energy supply to provide deployment energy in the event the vehicle voltage is low or lost during an accident.

ELECTRONIC CLIMATE CONTROL (ECC) PANEL
The ECC is used by the driver to control the air conditioner and heating system, also used to retrieve diagnostic information (i.e. trouble codes, sensor parameters, etc.), or override certain output components.

POWERTRAIN CONTROL MODULE (PCM)
The Powertrain Control Module is a computer that controls the multiport electronic fuel injection, ignition and emission control system. The PCM monitors operating conditions like engine speed/load and air/fuel ratio through various engine sensors, including an exhaust gas oxygen sensor, and controls the following:

^ Fuel Delivery (pump) and Fuel Injection System
^ Ignition / Electronic Spark Timing (EST)
^ Electronic Spark Control (ESC - knock sensor)
^ Air Conditioning Compressor Clutch
^ Coolant Fan
^ Idle Speed Control
^ Evaporative Emission Control System (purge control)
^ [1][2]Torque Converter Clutch. (TCC)
^ Electronically Controlled Automatic Transmission (shift control)

ON-BOARD SELF DIAGNOSTICS
The system has built-in diagnostics that recognizes problems in input/output devices and circuits. If a problem is detected, the system signals the driver by turning on the "SERVICE ENGINE SOON" (SES) light, located on the instrument panel. The light stays "ON" until the problem is repaired. Most malfunctions will store a trouble code in the computer memory that identifies the device or circuit where the fault was detected.

FAIL-SAFE OPERATION
The system also has a built in back-up system to provide near normal driving conditions during system malfunction. When problems are detected in certain systems, the PCM will revert to its fail-safe mode so the vehicle can be driven until repaired.

INSTRUMENT PANEL CLUSTER (IPC) - SERIAL DATA
During diagnostic mode the IPC is used to display BCM/PCM diagnostic codes, BCM/PCM data parameters, and discrete input and output values.

All components in the system are always in continuous communication with each other to provide accurate control over the many sub-systems involved. When one or more of these sub-system circuits exceeds pre-programmed limits a malfunction is indicated. when this occurs, the "SERVICE ENGINE SOON" warning lamp and a backup function may be activated until the malfunction is corrected.

CENTRAL POWER SUPPLY
Because the BCM and its sub-systems are electronic devices a Central Power Supply (CPS) is used. The CPS takes power from the vehicles battery and provides a voltage output that is isolated from electrical interference that may be produced during normal vehicle operation. It provides voltage output to the BCM and the IPC, and provides an isolated ground for the ECC, IPC, BCM, and the HVAC programmer.

HEATING, VENTILATION, AIR CONDITIONING PROGRAMMER
The HVAC programmer receives information from the ECC and carries out the commands necessary to obtain the correct interior temperature.