K 2500 Yukon 4WD V8-6.0L VIN U (2000)
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Contaminated fuel
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Running out of fuel
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Fuel fouled spark plugs
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Basic engine fault
Fuel Trim System Operation
The fuel trim system monitors the averages of short-term and long-term fuel trim values. If these fuel trim values stay at their limits for a calibrated
period of time, a malfunction is indicated. The fuel trim diagnostic compares the average of short and long-term fuel trim values. If either value is within
the thresholds, a pass is recorded. If either value is outside the thresholds, a rich or lean fuel trim DTC will set.
Comprehensive Component Monitor Diagnostic
Comprehensive component monitoring diagnostics are required to monitor emissions-related input and output powertrain components.
Input Components
The PCM monitors the input components for circuit continuity and out-of-range values. This includes performance checking. Performance checking
refers to indicating a fault when the signal from a sensor does not seem reasonable, such as a Throttle Position (TP) sensor that indicates high throttle
position at low engine loads or MAP voltage. The input components may include, but are not limited to, the following sensors:
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The Vehicle Speed (VSS) Sensor
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Mass Air Flow (MAF) sensor
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Intake Air Temperature (IAT) sensor
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Crankshaft Position (CKP) sensor
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Knock Sensor (KS)
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Throttle Position (TP) sensor
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Engine Coolant Temperature (ECT) sensor
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Camshaft Position (CMP) sensor
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Manifold Absolute Pressure (MAP) sensor
In addition to the circuit continuity and rationality check, the ECT sensor is monitored for its ability to achieve a steady state temperature to enable
Closed Loop fuel control.
Output Components
Diagnose the output components for the proper response to PCM commands. Components where functional monitoring is not feasible will be
monitored for circuit continuity and out-of-range values if applicable.
Output components to be monitored include, but are not limited to, the following circuits:
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The Idle Air Control (IAC) motor
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The EVAP system
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The electronic transmission controls
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The A/C relay, if so equipped
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The Vehicle Speed Sensor (VSS) output
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The Malfunction Indicator Lamp (MIL) control
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The cruise control enable, if so equipped
Wiring Harness Service
Replace the wire harnesses with the proper part number replacement. When splicing signal wires into a harness, use the wiring that has high temperature
insulation.
Consider the low amperage and voltage levels utilized in the powertrain control systems. Make the best possible bond at all splices. Use rosin-core solder
in these areas.
Molded-on connectors require complete replacement of the connector. Splice a new connector into the harness. Replacement connectors and terminals
are listed in Group 8.965 in the Standard Parts Catalog. For wiring repair, refer to Wiring Repairs in Diagrams.
Connectors and Terminals
In order to prevent shorting between opposite terminals, use care when probing a connector and when replacing terminals. Damage to the components
could result.
Always use jumper wires between connectors for circuit checking.
Never probe through Weather-Pack seals.
The J 35616-A connector test adapter kit, or the equivalent, contains an assortment of flexible connectors used to probe terminals during diagnosis. Fuse
