Powertrain Control Module (PCM)

Powertrain Control Module Connector Locations:

Description

The Powertrain Control Module (PCM) 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 PCM monitors numerous engine and vehicle functions.

Vehicle Control Center

The PCM is the control center of the vehicle. It controls the following:

^ Fuel metering system.

^ Transmission shifting.

^ Ignition timing.

^ On-board diagnostics for powertrain functions.

The PCM constantly looks at the information from various sensors, and controls the systems that affect vehicle performance. The PCM also performs the diagnostic function of the system. It can recognize operational problems. The PCM also alerts the driver through the MIL (Malfunction Indicator Lamp). When the PCM detects a malfunction, it stores a diagnostic trouble code (DTC). A DTC stored, will identify the problem areas. This will aid the technician in making repairs.

Construction

The PCM consists of two parts: a controller (the PCM without the Knock Sensor module) and the Knock Sensor module.

PCM Output Voltages

The PCM supplies either 5 or 12 volts to power various sensors or switches. This is done through resistances in the PCM. The resistance is so high in value that a test light will not light when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because its resistance is too low. Therefore, a digital voltmeter (J 39200) with at least 10 megohms input impedance is required to ensure accurate voltage readings.

PCM Output Circuits
The PCM controls output circuits such as the injectors, IAC, cooling fan relays, etc. by controlling the ground or power feed circuit through transistors or a device called an Output Driver Module.

The PCM also controls the following operations:

^ Fuel control

^ Ignition Control (IC)

^ Knock Sensor (KS) system

^ Automatic transmission shift functions

^ Cruise Control Enable

^ Generator

^ Evaporative Emission (EVAP) Purge

^ A/C Clutch Control

^ Cooling Fan Control

Control Module Function

The PCM 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.