Express 4500 V8-6.0L (2010)
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 low 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 low speed GMLAN serial data circuit between the splice pack and a module will only affect that specific module. This type of
failure will set a loss of communication DTC for each module effected, and the other modules will still communicate.
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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 No CANdi Module Detected message will be displayed.
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An open between the DLC and JX 200 will only effect the communication with the scan tool. The vehicle modules will still communicate, and the
vehicle will start.
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The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuit.
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Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed LAN
communications with the scan tool.
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 light.
Reference Information
Schematic Reference
Data Communication Schematics (See: Diagrams/Electrical Diagrams)
Connector End View Reference
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Component Connector End Views (See: Diagrams/Connector Views/Connector End Views By Name)
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Splice Pack Connector End Views (See: Diagrams/Connector Views/Splices By Number)
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)
Circuit/System Testing
Note: Use the schematic to identify the following:
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Control modules the vehicle is equipped with
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Control module locations on the low speed GMLAN serial data circuit
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The low speed GMLAN serial data circuit terminals for each control module
1. Attempt to communicate with all control modules on the low 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 low speed GMLAN
serial data circuit.
‹› If only one control module is not communicating, diagnose that control module only. Refer to DTC U0100-U02FF (See: Testing and
Inspection/Diagnostic Trouble Code Tests and Associated Procedures/U Code Charts/U0100).
‹› If one or more control modules are communicating but not all, refer to Testing the Serial Data Circuit for an Open/High Resistance.
2. Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
3. All access doors closed, ignition OFF for 60 seconds, test for less than 10 ohm between the ground circuit terminal 5 and ground.
