the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,
and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.
6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup
circuit terminal and ground.
锟斤拷If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:
* Class 2 serial data circuit terminal 2
* Low speed GMLAN serial data terminal 1
* High speed GMLAN serial data terminal 6 or 14
锟斤拷If greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module
and a control module setting the DTC or a serial data splice pack.
8. If all circuits test normal, replace the control module that is not communicating.
Repair Instructions
Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.
* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic
Procedures/Wiring Repairs/GMLAN Wiring Repairs)
* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and
programming
U029D
DTC U0100-U02FF (without HP2)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System
Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an
overview of the diagnostic approach.
* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure
Instructions) provides an overview of each diagnostic category.
DTC Descriptor
Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).
Diagnostic Fault Information
Circuit/System Description
The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the
serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic
trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health
