K 2500 Yukon 4WD V8-6.0L VIN U (2000)
Powertrain Control Module: Description and Operation
Powertrain Control Module
Circuit Description
The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. To provide optimum driveability and
emissions, the PCM monitors input signals from the following components in calculating Ignition Control (IC) spark timing:
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The Engine Coolant Temperature (ECT) sensor
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The Intake Air Temperature (IAT) sensor
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The Mass Air Flow (MAF) sensor
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The trans range inputs from the transmission range switch (PRND)
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The Throttle Position (TP) sensor
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The Vehicle Speed Sensor (VSS)
General Description
Powertrain Control Module
The Powertrain Control Module (PCM) is located in the engine compartment. The PCM is the control center of the vehicle. It controls the following:
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The fuel metering system
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The transmission shifting
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The ignition timing
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The on-board diagnostics for powertrain functions
The PCM constantly monitors the information from various sensors and controls the systems that affect vehicle performance and emissions. The PCM
also performs the diagnostic functions for those systems. The PCM can recognize operational problems and alert the driver through the Malfunction
Indicator Lamp (MIL) when a malfunction has occurred. When a malfunction is detected, the PCM stores a Diagnostic Trouble Code (DTC) which
helps to identify problem areas. This is done to aid the technician in making repairs.
The PCM supplies either 5.0 or 12.0 volts to power vaccum sensors and switches. This is done through resistance's in the PCM. The resistance is so high
in value that a test lamp does not illuminate when connected to the circuit. In some cases, even an ordinary shop voltmeter does not give an accurate
reading because the voltmeters resistance is too low. Therefore, a DMM with a minimum of 10 megaohms input impedance is required to ensure
accurate voltage readings.
The PCM controls output circuits such as the fuel injectors, the Idle Air Control (IAC), the cooling fan relays, etc. by controlling the ground or the
power feed circuit through transistors or a device called an output driver module.
