Engine Control Module: Description and Operation

The Powertrain Control Module (PCM) is the control center of the vehicle. It controls the following items:
^ Fuel metering system.
^ Transaxle/transmission shifting.
^ Ignition timing.
^ On-board diagnostics for powertrain functions.

It 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, alert the driver through the MIL, and store diagnostic trouble codes which identify the problem areas to aid the technician in making repairs.

The type of PCM used is a PCM 32U. For service, the PCM consists of two parts: a controller (the PCM without the Knock Sensor module) and the Knock Sensor module.

The Control Module refers to the Powertrain Control Module (PCM) or the Vehicle Control Module (VCM). 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 (if so equipped)
^ Evaporative Emission (EVAP) Purge
^ A/C Clutch Control
^ Cooling Fan Control

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.

REFERENCE LOW
This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the ignition control module. Although this circuit is electrically connected to the PCM, it is not connected to ground at the PCM. The PCM compares voltage pulses on the 18X and 3X reference input circuits to any on this circuit, ignoring pulses that appear on both. If the circuit is open, or connected to ground at the PCM, it may cause poor engine performance and possibly a MIL with no DTC set.