U1500

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

This DTC indicates an internal fault and is set within the vehicle communication interface module (VCIM). No external circuits are involved.


Conditions for Running the DTC

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


Conditions for Setting the DTC

The VCIM detects an internal communication malfunction.


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

* A current DTC clears when the malfunction is no longer present.
* A history DTC clears after 50 malfunction-free ignition cycles.



Diagnostic Aids

The diagnostic procedure used for DTC U1500 in OnStar(R) systems with single module generations of OnStar(R) differ greatly from previous generations with 2 modules. While these older generations denoted a failure of the 3 wire bus between the modules by setting a U1500, single module OnStar(R) systems use this DTC to denote an internal module failure. The determination of whether a 1 or 2 module generation of OnStar(R) is used should be confirmed. Refer to OnStar Description and Operation (OnStar Description and Operation) .


Reference Information
Schematic Reference

OnStar Schematics (OnStar Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
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)
* OnStar Description and Operation (OnStar Description and Operation)



Circuit/System Verification

1. Ignition ON, verify DTC U1500 is set as current.

• If DTC U1500 is not current, refer to Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics) .

2. 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