Cellular, Entertainment, and Navigation

DTC U1500

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC U1500
- Inter-Device Dedicated Bus Malfunction




Circuit/System Description

DTC U1500 sets when an internal fault is detected within the vehicle communication interface module (VCIM). No external circuits are involved.


Conditions for Running the DTC

* Ignition ON.
* Battery voltage must be between 9-16 volts.



Conditions for Setting the DTC

The VCIM runs the program to detect an internal faults during module power up and every 10 seconds thereafter until the module re-enters the sleep mode.


Action Taken When the DTC Sets

* The OnStar(R) status LED turns red.
* The vehicle is unable to connect to the OnStar(R) Call Center.



Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.



Reference Information
Schematic Reference

OnStar Schematics (OnStar Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

OnStar Description and Operation (OnStar Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Testing

Ignition ON, with a scan tool, clear all DTCs and operate the audio system within the Conditions for Running the DTC.

If the DTC resets, replace the VCIM.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.


Control Module References (Programming and Relearning) for VCIM replacement, setup, and programming