Equinox AWD V6-3.4L (2008)
Engine Control Module: Description and Operation
Engine Control Module Description
The engine control module (ECM) interacts with many emission related components and systems, and monitors the emission related components and
systems for deterioration. OBD II diagnostics monitor the system performance and a diagnostic trouble code (DTC) sets if the system performance
degrades.
The malfunction indicator lamp (MIL) operation and the DTC storage are dictated by the DTC type. A DTC is ranked as a Type A or Type B if the DTC
is emissions related. Type C is a non-emissions related DTC.
The ECM is in the engine compartment. The ECM is the control center of the engine controls system. The ECM controls the following components:
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The fuel injection system
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The ignition system
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The emission control systems
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The on-board diagnostics
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The A/C and fan systems
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The throttle actuation control (TAC) system
The ECM constantly monitors the information from various sensors and other inputs, and controls the systems that affect the vehicle performance and the
emissions. The ECM also performs diagnostic tests on various parts of the system. The ECM can recognize operational problems and alert the driver via
the MIL. When the ECM detects a malfunction, the ECM stores a DTC. The condition area is identified by the particular DTC that is set. This aids the
technician in making repairs.
ECM Function
The engine control module (ECM) can supply 5 volts or 12 volts to the various sensors or switches. This is done through pull-up resistors to the
regulated power supplies within the ECM. In some cases, even an ordinary shop voltmeter will not give an accurate reading because the resistance is too
low. Therefore, a DMM with at least 10 megaohms input impedance is required in order to ensure accurate voltage readings.
The ECM controls the output circuits by controlling the ground or the power feed circuit through the transistors or a device called an output driver
module.
EEPROM
The electronically erasable programmable read only memory (EEPROM) is a permanent memory that is physically part of the engine control module
(ECM). The EEPROM contains program and calibration information that the ECM needs in order to control the powertrain operation.
Special equipment, as well as the correct program and calibration for the vehicle, are required in order to reprogram the ECM.
Data Link Connector (DLC)
The data link connector (DLC) is a 16-pin connector that provides the technician a means of accessing serial data for aid in the diagnosis. This connector
allows the technician to use a scan tool in order to monitor the various serial data parameters, and display the DTC information. The DLC is located
inside of the drivers compartment, underneath the dash.
Malfunction Indicator Lamp (MIL)
The malfunction indicator lamp (MIL) is inside of the instrument panel cluster (IPC). The MIL is controlled by the engine control module (ECM) and
illuminates when the ECM detects a condition that affects the vehicle emissions.
ECM Service Precautions
The engine control module (ECM), by design, can withstand the normal current draws that are associated with the vehicle operations. However, care
must be used in order to avoid overloading any of these circuits. When testing for opens or shorts, do not ground or apply voltage to any of the ECM
circuits unless the diagnostic procedure instructs you to do so. These circuits should only be tested with a DMM.
Emissions Diagnosis For State I/M Programs
This OBD II equipped vehicle is designed to diagnose any conditions that could lead to excessive levels of the following emissions:
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Hydrocarbons (HC)
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Carbon monoxide (CO)
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Oxides of nitrogen (NOx)
