Automatic Transmission

System Diagram (A/T):

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, automatic transmission operation, 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 the event of certain system failures, the 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:

^ Crankshaft Position Sensor
^ Vehicle Speed Sensor
^ Airflow Sensor
^ Engine Coolant Temperature Sensor (CIS)
^ Engine Coolant Temperature Sensor (Fan)
^ Intake Air Temperature Sensor
^ Throttle Position Sensor
^ Barometric Atmospheric Presure Sensor
^ Heated Oxygen Sensor
^ Closed Loop System (Oxygen Sensor Output)
^ Vehicle Speed Pulse Generator (A/T)
^ ATF Thermosensor
^ A/T Control Solenoids

ON-BOARD DIAGNOSTICS
The system 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 engine is running), alerting the driver to seek service. The technician can then extract trouble codes from the PCME to aid in the performance of efficient troubleshooting and repair.

Components can be grouped as PCME input and output devices. Not all devices are monitored by the on-board diagnostic system.

INPUT DEVICES
Input devices control or produce PCME monitored voltage signals.

^ Main Relay
^ Ignition Switch
^ Data Link Connector
^ Daytime Running Lights (Canada)
^ Rear Window Defroster Relay
^ Vehicle Speed Sensor (Code 6)
^ Idle Switch
^ Stoplight Switch
^ Steering Pressure Sensor
^ Air Conditioning Sensor
^ Blower Control Switch
^ Headlight Switch
^ Park/Neutral and Clutch Switches (M/T)
^ Distributor (NE Signal) (Code 2)
^ Distributor (G Signal) (Code 3)
^ Engine Coolant Temperature Sensor (Fan) (Code 69)
^ Engine Coolant Temperature Sensor (CIS) (Code 9)
^ EGR Function Sensor (Calif. Only)
^ Intake Air Temperature Sensor (Code 10)
^ Throttle Position Sensor (TVO) (Code 12)
^ Heated Oxygen Sensor (Codes 15 & 17)
^ Airflow Sensor (Code 8)
^ Hold Mode Switch (A/T)
^ Inhibitor Switch (A/T)
^ Barometric Absolute Pressure Sensor (A/T) (Code 14)
^ Oil (ATF) Thermosensor (A/T) (Code 56)
^ Vehicle Speed Pulse Generator (A/T) (Code 55)

OUTPUT DEVICES
Output devices are PCME controlled components.

^ Data Link Connector
^ Fuel Pump Relay
^ A/C relay
^ Coolant Fan Relay
^ Coolant Fan Relays 1, 2, & 3 (A/T) (Codes 67 & 68)
^ Igniter
^ Throttle Position Sensor
^ Solenoid Valve (EGR) (Code 28)
^ Solenoid Valve (Pressure Regulator) (Code 25)
^ Solenoid Valve (Purge Control) (Code 26)
^ Fuel Injectors
^ Idle Air Control Valve (Code 34)
^ HOLD Indicator (A/T)
^ Transmission Control Solenoid Valves (A/T) (Codes 60 - 66)