General System
System Diagram:
PURPOSE
The Powertrain Control Module (PCME) is the central component of this computerized fuel, ignition and emission control system. To maintain fuel economy, good driveability and reduced vehicle emissions, the PCME monitors data from various sensors and controls functions such as the fuel injection system (air/fuel ratio), emission control devices and on-board diagnostics.
The PCME is a computer that judges air/fuel ratio as rich or lean according to a voltage signal generated by an oxygen sensor. Based on oxygen sensor and other input data, the PCME generates a controlling signal to the fuel injectors that regulates "ON" time. Because fuel pressure remains constant, the PCME controls air/fuel ratio adjustments by varying injector "ON" time.
FAIL-SAFE MODE
To provide a margin of safety by maintaining driveability in event of certain system failures, PCME has a fail-safe mode of preprogrammed values. PCME output will automatically switch to fail-safe mode if a fault is detected in any of these components and/or systems:
^ Airflow meter
^ Atmospheric pressure sensor
^ Feedback system
^ Intake air thermosensor
^ Oxygen sensor
^ Throttle sensor
^ Water thermosensor
ON-BOARD DIAGNOSTICS
PCME incorporates self-diagnostic capability monitored via a dash mounted malfunction indicator lamp (MIL). When the system detects a fault in a monitored component and/or circuit, the lamp will light ("CHECK") and stay on (while the engine is running), alerting the driver to seek service. The technician can then extract PCME trouble codes to aid in troubleshooting and repair.
Components can be grouped as PCME input and output devices. Input devices control or produce PCME monitored voltage signals. Output devices are components PCME controlled. Not all of these devices are monitored by the on-board diagnostic system.
INPUT DEVICES
^ A/C switch
^ Airflow sensor (code 08)
^ Atmospheric pressure sensor (code 14)
^ Central processing unit (electrical load signal)
^ Distributor
-G signal (code 03)
-Ne signal (code 02)
^ Feedback system (code 17)
^ Idle switch
^ Ignition switch ("START" and "ON" positions)
^ Inhibitor switch (A/T)
^ Intake air thermosensor (code 11)
^ Neutral and clutch switches (M/T)
^ Oxygen sensor (code 15)
^ Power steering pressure switch
^ Speed sensor (A/T)
^ Stop light switch (M/T)
^ Test connector
^ Throttle sensor (code 12)
^ Water thermosensor (code 09)
OUTPUT DEVICES
^ A/C relay/cut-off
^ Airflow sensor (burn-off)
^ Bypass air control (BAC) valve
-Air valve
-Idle speed control (ISC) valve (code 34)
^ Circuit opening relay (fuel pump control)
^ 4A/T control unit (lockup inhibition control)
^ Fuel injectors/injection timing
^ Igniter
^ Malfunction indicator lamp (MIL)
^ Pressure regulator solenoid valve (code 25)
^ Purge control solenoid valve (code 26)