Yukon XL 4WD V8-5.3L (2011)
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 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 ECM is part of a network and communicates with various other vehicle control modules.
Malfunction indicator lamp (MIL) operation and 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 the control center of the engine controls system. Review the components and wiring diagrams in order to determine which systems are
controlled by the ECM.
The ECM constantly monitors the information from various sensors and other inputs, and controls the systems that affect engine performance and
emissions. The ECM also performs diagnostic tests on various parts of the system and can turn on the MIL when it recognizes an operational problem
that affects emissions. 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 ECM can supply 5 V or 12 V to various sensors or switches. This is done through pull-up resistors to regulated power supplies within the ECM. In
some cases, even an ordinary shop voltmeter will not give an accurate reading due to low input resistance. Therefore, a digital multimeter (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 transistors or a device called an output driver module.
EEPROM
The electronically erasable programmable read only memory (EEPROM) is an integral part of the ECM. The EEPROM contains program and
calibration information that the ECM needs in order to control engine 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) provides serial data communication for ECM diagnosis. This connector allows the technician to use a scan tool in order
to monitor various serial data parameters, and display DTC information. The DLC is located inside the driver's compartment, underneath the dash.
Malfunction Indicator Lamp (MIL)
The malfunction indicator lamp (MIL) is inside the instrument panel cluster (IPC). The MIL is controlled by the ECM and illuminates when the ECM
detects a condition that affects vehicle emissions.
ECM Service Precautions
The ECM, by design, can withstand normal current draws that are associated with 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 unless the diagnostic procedure instructs otherwise.
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:
*
Hydrocarbons (HC)
*
Carbon monoxide (CO)
*
Oxides of nitrogen (NOx)
*
Evaporative emission (EVAP) system losses
Should this vehicle's on-board diagnostic system (ECM) detect a condition that could result in excessive emissions, the ECM turns ON the MIL and
stores a DTC that is associated with the condition.
Aftermarket (Add-On) Electrical And Vacuum Equipment
Caution: Do not attach add-on vacuum operated equipment to this vehicle. The use of add-on vacuum equipment may result in damage to vehicle
