K 2500 Yukon 4WD V8-6.0L VIN U (2000)
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.
Use of Circuit Testing Tools
Do not use a test lamp in order to diagnose the powertrain electrical systems unless specifically instructed by the diagnostic procedures. Use the J
35616-A connector test adapter kit whenever diagnostic procedures call for probing any connectors.
Basic Knowledge Required
Without a basic knowledge of electricity, it will be difficult to use the diagnostic procedures contained in this section. 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.
After Market (Add-on) Electrical and Vacuum Equipment
After market, add-on electrical and vacuum equipment is defined as any equipment installed on a vehicle after leaving the factory that connects to the
vehicles electrical or vacuum systems. No allowances have been made in the vehicle design for this type of equipment.
NOTE:
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Do not attach add-on vacuum operated equipment to this vehicle. The use of add-on vacuum equipment may result in damage to vehicle
components or systems.
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Connect any add-on electrically operated equipment to the vehicle's electrical system at the battery (power and ground) in order to prevent damage
to the vehicle.
Add-on electrical equipment, even when installed to these strict guidelines, may still cause the powertrain system to malfunction. This may also include
equipment not connected to the vehicles electrical system such as portable telephones and radios.
Therefore, the first step in diagnosing any powertrain problem is to eliminate all after market electrical equipment from the vehicle. After this is done, if
the problem still exists, diagnose the problem in the normal manner.
Electrostatic Discharge Damage
NOTE: In order to prevent possible Electrostatic Discharge damage to the PCM, Do Not touch the connector pins or the soldered components on the
