K 1500 Yukon 4WD V8-4.8L VIN V (2003)
Engine Control Module: Description and Operation
Powertrain
POWERTRAIN
The powertrain has electronic controls to reduce exhaust emissions while maintaining excellent driveability and fuel economy. The powertrain control
module (PCM) is the control center of this system. The PCM monitors numerous engine and vehicle functions. The PCM constantly looks at the
information from various sensors and other inputs, and controls the systems that affect vehicle performance and emissions. The PCM also performs the
diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the malfunction indicator lamp
(MIL). When the PCM detects a malfunction, the PCM stores a diagnostic trouble code (DTC). The problem area is identified by the particular DTC
that is set. The control module supplies a buffered voltage to various sensors and switches. Review the components and wiring diagrams in order to
determine which systems are controlled by the PCM.
The following are some of the functions that the PCM controls:
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The engine fueling
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The ignition control (IC)
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The knock sensor (KS) system
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The evaporative emissions (EVAP) system
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The secondary air injection (AIR) system (if equipped)
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The exhaust gas recirculation (EGR) system
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The automatic transmission functions
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The generator
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The A/C clutch control
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The cooling fan control
POWERTRAIN CONTROL MODULE FUNCTION
The PCM constantly looks at the information from various sensors and other inputs and controls systems that affect vehicle performance and emissions.
The PCM also performs diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the
malfunction indicator lamp (MIL). When the PCM detects a malfunction, the PCM stores a diagnostic trouble code (DTC). The problem area is
identified by the particular DTC that is set. The control module supplies a buffered voltage to various sensors and switches. The input and output devices
in the PCM include analog-to-digital converters, signal buffers, counters, and output drivers. The output drivers are electronic switches that complete a
ground or voltage circuit when turned on. Most PCM controlled components are operated via output drivers. The PCM monitors these driver circuits for
proper operation and, in most cases, can set a DTC corresponding to the controlled device if a problem is detected.
Throttle Actuator Control Module
The PCM determines the driver's intent and then calculates the appropriate throttle response. This information is sent to the TAC module through a
dedicated serial data line.
Electronic Ignition System
The PCM controls all ignition system functions, and constantly corrects the basic spark timing.
The PCM monitors information from various sensor inputs that include the following:
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The throttle position (TP) sensor
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The engine coolant temperature (ECT) sensor
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The mass airflow (MAF) sensor
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The intake air temperature (IAT) sensor
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The vehicle speed sensor (VSS)
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The transmission gear position or range information sensors
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The engine knock sensors (KS)
MALFUNCTION INDICATOR LAMP (MIL) OPERATION
The malfunction indicator lamp (MIL) is located in the instrument panel cluster. The MIL will display as either SERVICE ENGINE SOON or one of the
following symbols when commanded ON:
