Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC U1500: Inter-Device Dedicated Bus MalfunctionCircuit/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® status LED turns red. |
| • | The vehicle is unable to connect to the OnStar® 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® systems with single module generations of OnStar® 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® systems use this DTC to denote an internal module failure. The determination of whether a 1 or 2 module generation of OnStar® is used should be confirmed. Refer to OnStar Description and Operation .
Reference Information
Schematic Reference
Connector End View Reference
Entertainment/Communication Connector End Views
Electrical Information Reference
Circuit/System Verification
- Ignition ON, verify DTC U1500 is set as current.
- Replace the VCIM.
| ⇒ | If DTC U1500 is not current, refer to Testing for Intermittent Conditions and Poor Connections . |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for VCIM replacement, setup, and programming
