Sierra 1500 2WD V6-4.3L (2008)
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Use the 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 221 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.
Circuit/System Testing
1. Test for less than 1 ohm between the DLC ground circuit terminal 5 and ground.
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If greater than the specified range, test the ground circuit for open/high resistance.
2. Ignition OFF, disconnect the harness connector at splice pack JX 221.
3. Ignition ON, with a scan tool, attempt to communicate with the instrument panel cluster (IPC). Communication should be available.
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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.
4. Install a 3-amp fused jumper wire between terminal A and terminal M of the splice pack. Install another 3-amp fused jumper wire to terminal L.
5. Using the open end of the jumper wire at terminal L, connect to splice pack terminals B through K and attempt to establish communications with
each module connected to the splice pack, one at a time. Each module should be able to communicate.
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If communications cannot be established with any module after connecting an individual module, replace the module that caused the no
communication.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair. See: Testing and Inspection/Diagnostic Trouble Code Tests and Associated
Procedures/Verification Tests and Procedures
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GMLAN Wiring Repairs
Scan Tool Does Not Power Up
Scan Tool Does Not Power Up
Diagnostic Instructions
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Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and
Diagnostic Overview/Diagnostic System Check - Vehicle
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Review Strategy Based Diagnosis for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
