Silverado 1500 4WD V8-5.3L (2007)
Information Bus: Testing and Inspection
Scan Tool Does Not Communicate with Low Speed GMLAN Device
Scan Tool Does Not Communicate with Low Speed GMLAN Device
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
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 SP203 as the common connection between the modules and the data link connector (DLC).
Diagnostic Aids
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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 C 203 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.
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Use the DMM MIN/MAX function to capture/locate intermittent conditions.
Circuit/System Testing
1. Test for less than 1 ohm of resistance between the DLC ground circuit terminal 5 and ground.
‹› If greater than 1 ohm, test the ground circuit for open/high resistance.
2. Ignition OFF, disconnect the harness connector at splice pack SP 300.
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
