General System Description

The Control Module refers to the Powertrain Control Module (PCM). The control module is designed to maintain exhaust emission levels to Federal or California standards while providing excellent driveability and fuel efficiency. Review the components and wiring diagrams in order to determine which systems are controlled by each specific control module. The control module monitors numerous engine and vehicle functions. The control module controls the following operations:

^ Fuel control
^ Ignition Control (IC)
^ Knock Sensor (KS) system
^ Automatic transmission shift functions
^ Cruise Control Enable (if so equipped)
^ Generator
^ Evaporative Emission (EVAP) Purge
^ A/C Clutch Control
^ Cooling Fan Control

INPUT COMPONENTS
The Control Module monitors the input components for circuit continuity and out-of-range values. This includes performance checking. Performance checking refers to indicating a fault when the signal from a sensor does not seem reasonable (i.e. a Throttle Position (TP) sensor that indicates high throttle position at low engine loads or MAP voltage). The input components may include but are not limited to the following sensors:

^ The Vehicle Speed Sensor (VSS)
^ The Crankshaft Position (CKP) sensor
^ The Knock Sensor (KS)
^ The Throttle Position (TP) sensor
^ The Engine Coolant Temperature (ECT) sensor
^ The Camshaft Position (CM P) sensor
^ The Manifold Absolute Pressure (MAP) sensor
^ The Mass Air Flow (MAF) sensor In addition to the circuit continuity and rationality check, the ECT sensor is monitored for its ability to achieve a steady state temperature to enable closed loop fuel control.


OUTPUT COMPONENTS
Diagnose the output components for the proper response to control module commands. Components where functional monitoring is not feasible will be monitored for circuit continuity and out-of-range values if applicable.

Output components to be monitored include, but are not limited to the following circuits:

^ The Idle Air Control (IAC) Motor
^ The Control module controlled EVAP Canister Purge Valve
^ The Electronic transmission controls
^ The A/C relay
^ The Cooling fan relay
^ The VSS output
^ The MIL control
^ The Cruise control inhibit

CONTROL MODULE FUNCTION
The Control Module supplies a buffered voltage to various sensors and switches. The input and output devices in the control module include an analog to digital converters, signal buffers, counters, and special drivers. The Control Module controls most components with electronic switches which complete a ground circuit when turned ON. These switches are arranged in groups of 4 and 7 called one of the following:

^ Quad Driver Module
^ Output Driver Modules

The surface mounted Quad Driver Module can independently control up to 4 outputs (Control Module) terminals. The Output Driver Modules can independently control up to 7 outputs. Not all outputs are always used.

INFORMATION SENSORS
All of the sensors and input switches can be diagnosed using a scan tool. The following is a short description of how the sensors and switches can be diagnosed by using a scan tool. The scan tool can also be used to compare the values for a normal running engine with the engine being diagnosed.