Yukon Denali 2WD V8-6.0L Hybrid (2010)
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A control module on the data communication circuit was disconnected while the communication circuit is awake.
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Power to one or more modules was interrupted during diagnosis
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A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
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Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
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If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.
These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
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Do not replace a control module reporting a U code. The U code identifies which control module needs to be diagnosed for a communication
issue.
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Communication may be available between the BCM and the scan tool with the Powertrain High Speed GMLAN serial data system inoperative.
This condition is due to the BCM using both the high and low speed GMLAN systems.
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An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. When the scan tool
attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed.
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The engine will not start when there is a total malfunction of the Powertrain High Speed GMLAN serial data bus.
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Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed GMLAN
communications with the scan tool.
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The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
These conditions may be caused by the installation of an aftermarket navigation radio module (see bulletins). Some customers may comment of
one or more of the following concerns:
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Vehicle will not crank.
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Vehicle cranks but will not start.
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Vehicle stability enhancement system warning lights and messages.
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PRNDL gear indicator position errors.
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Tire Pressure Monitor (TPM) system warning lights.
Reference Information
Schematic Reference
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Data Communication Schematics (See: Diagrams/Electrical Diagrams)
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Control Module References (See: Testing and Inspection/Programming and Relearning)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views)
Description and Operation
Data Link Communications Description and Operation (See: Description and Operation)
Electrical Information Reference
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Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit
Testing/Circuit Testing)
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Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Connector
Repairs/Connector Repairs)
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Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General
Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)
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Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring
Repairs/Wiring Repairs)
Scan Tool Reference
Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information
Circuit/System Testing
Note: Each control module may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following:
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Control modules the vehicle is equipped with
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Powertrain High Speed GMLAN serial data circuit terminating resistors
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Control module locations on the Powertrain High Speed GMLAN serial data circuits
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Each control module's Powertrain High Speed GMLAN serial data circuit terminals
1. Attempt to communicate with all control modules on the Powertrain High Speed GMLAN serial data circuit, refer to Data Link References (See:
Initial Inspection and Diagnostic Overview). Communications should not be available with two or more control modules on the Powertrain High
Speed GMLAN serial data circuit.
