H2 V8-6.2L (2008)
Circuit/System Description
Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating
information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial
data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate.
The low speed GMLAN serial data circuit uses JX 205 as the common connection between the modules and the data link connector (DLC).
Diagnostic Aids
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Use the Data Link References (See: Initial Inspection and Diagnostic Overview/Data Link References) to identify the low speed GMLAN serial
data modules.
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This test is used for a total low speed GMLAN communication failure. If only 1 module is not communicating and sets no DTC, ensure that the
vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
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An open in the low speed GMLAN serial data circuit between the splice pack and a module will only effect the 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 to set up the vehicle on the tool and then not communicate with
the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module
detected" and will not communicate.
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An open between the DLC and JX 205 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.
The following conditions may cause a total loss of low speed GMLAN data communication:
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The low speed GMLAN serial data circuit shorted to ground or voltage.
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A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuit.
Reference Information
Schematic Reference
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Body Control System Schematics (See: Body and Frame/Body Control Systems/Diagrams/Electrical Diagrams)
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Data Communication Schematics (See: Diagrams/Electrical Diagrams)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views/Component Connector End Views)
Description and Operation
Data Link Communications Description and Operation (See: Description and Operation)
Electrical Information Reference
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Circuit Testing (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Circuit Testing/Circuit Testing)
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Connector Repairs (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Connector Repairs/Connector Repairs)
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Testing for Intermittent Conditions and Poor Connections (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Circuit
Testing/Testing For Intermittent and Poor Connections)
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Wiring Repairs (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Wiring Repairs/Wiring Repairs)
Scan Tool Reference
Programming and Relearning (See: Testing and Inspection/Programming and Relearning)for scan tool information
Circuit/System Testing
1. Test for less than 1 ohm between the DLC ground circuit terminal 5 and ground.
‹› If greater than The specified range, test the ground circuit for open/high resistance.
2. Ignition OFF, disconnect the JX 205 harness connector at the splice pack.
3. Ignition ON, with a scan tool, attempt to communicate with the instrument panel cluster (IPC). Communication should be available.
‹› If no communication, disconnect the modules still connected to the DLC one at a time, starting with the furthest from the DLC and attempt to
communicate after each disconnect. When communication occurs, test the serial data circuit for a short to ground and a short to voltage
between the last module disconnected and the previous module disconnected. If the circuit tests normal, replace the last module disconnected.
If no communication is possible, test the serial data circuit for a short to ground, a short to voltage or an open/high resistance between the last
module disconnected and the DLC. If the circuit tests normal, replace the last module disconnected.
