U1500 Inter-Device Dedicated Bus Malfunction

Diagnostic Chart:

CIRCUIT DESCRIPTION
The DTC U1500 is an internal function of the vehicle interface unit (VIU). The DTC U1500 is set when the VIU detects no communication between the VIU and the vehicle communication unit (VCU).

CONDITIONS FOR RUNNING THE DTC
The ignition must be in the RUN or ACC position and the VIU power must be on. The VIU will run this test every 300 ms. Battery voltage must be at least 9.5 volts and no more than 15.5 volts.

ACTION TAKEN WHEN THE DTC SETS
When DTC U1500 is current the VIU does not communicate with the VCU.

CONDITIONS FOR CLEARING THE MIL/DTC
The code can be cleared when the VIU does not detect a failure during the last diagnostic cycle.

TEST DESCRIPTION
The number(s) below refer to the step number(s) on the diagnostic table.
2. This step test for proper operation of the OnStar(R) system.
4. This step tests for an open in the battery positive circuit between the VIU and the VCU.
5. This step tests for an open or a short to battery positive.
7. This step tests for an open or a short to battery positive.