K 1500 Yukon Denali AWD V8-6.0L VIN U (2002)
Torque Management
Torque management is a function of the PCM that reduces engine power under certain conditions. Torque management is performed for the following
reasons:
1. To prevent over-stressing the powertrain and driveline components
2. To prevent damage to the vehicle during certain abusive maneuvers
3. To reduce engine speed when the IAC is out of the normal operating range
The PCM monitors the following sensors and engine parameters in order to calculate engine output torque:
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The air/fuel ratio
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The Mass Air Flow (MAF) sensor
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The Manifold Absolute Pressure (MAP) Sensor
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The Intake Air Temperature (IAT) Sensor
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The spark advance
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The engine speed
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The Engine Coolant Temperature (ECT) Sensor
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The A/C clutch status
The PCM monitors the torque converter status, the transmission gear ratio, and the engine speed in order to determine if torque reduction is required.
The PCM retards the spark as appropriate to reduce engine torque output if torque reduction is required. The PCM also shuts OFF the fuel to certain
injectors in order to reduce the engine power in the case of an abusive maneuver.
The following are instances when engine power reduction is likely to be experienced:
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During transmission upshifts and downshifts
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During heavy acceleration from a standing start
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When the clutch pedal is released too quick under a heavy load, 6.0L only
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When one set of drive axles looses traction while the other set of drive axles are not moving, 4 Wheel Drive only and in 4WD low
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If the IAC is out of the normal operating range, except 6.0L
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When the driver is performing harsh or abusive maneuvers such as shifting into gear at high throttle angles or shifting the transmission from
reverse to drive to create a rocking motion
The driver is unlikely to notice the torque management actions in the first 2 instances. The engine power output is moderate at full throttle in the other
cases.
The PCM calculates the amount of spark retard necessary to reduce the engine power by the desired amount. The PCM disables the fuel injectors for
cylinders 1, 4, 6, and 7 in the case of an abusive maneuver.
Basic Knowledge Required
Without a basic knowledge of electricity, you will have difficulty using the diagnostic procedures. You should understand the basic theory of electricity
and know the meaning of voltage-volts, current-amps, and resistance-ohms. You should understand what happens in a circuit with an open or a shorted
wire. You should be able to read and understand a wiring diagram.
PCM Service Precautions
The PCM is designed to withstand normal current draws associated with vehicle operations. Avoid overloading any circuit. When testing for opens or
shorts, do not ground any of the PCM circuits unless instructed. When testing for opens or shorts, do not apply voltage to any of the PCM circuits unless
instructed. Only test these circuits with a DMM while the PCM connectors remain connected.
Engine Controls Information
The driveability and emissions information describes the function and operation of the powertrain control module (PCM).
The engine controls Information contains the following:
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Component locations
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Wiring diagrams
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PCM terminal end view and terminal definitions
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Diagnostic System Check-Computers and Controls Systems
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Diagnostic trouble code (DTC) tables
The component system includes the following items:
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Component and circuit description
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On-vehicle service for each sub-system
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Functional checks and diagnostic tables
The DTCs also contain diagnostic support information containing circuit diagrams, circuit or system information, and helpful diagnostic information.
System Status and Drive Cycle For Inspection/Maintenance
The System Status selection is included in the scan tool System Info menu.
Several states require that the I/M (OBD II system) pass on-board tests for the major diagnostics prior to having a vehicle emission inspection. This is
