Diagnostic Instructions
DTC Descriptors
DTC B128A 01: Mono Audio Signal Circuit Short to Battery
DTC B128A 02: Mono Audio Signal Circuit Short to Ground
Circuit/System Description
When a OnStar® key press is made, a serial data message is sent to the audio system to mute all radio functions and transmit OnStar® originated audio. After the audio is muted, the OnStar® signals are transmitted to the audio system
on the mono audio signal out circuit, and returned to the module on the mono audio signal in circuit.
Conditions for Running the DTC
The following are conditions that must be present in order for the navigation radio to enable diagnostics:
| • | The ignition must be in the RUN or ACC position. |
| • | The system voltage is at least 9.5 volts and no more than 15.5 volts. |
Conditions for Setting the DTC
| • | The navigation radio detects a short to battery on the mono audio signal circuit. |
| • | The navigation radio detects a short to ground on the mono audio signal circuit. |
| • | All the above conditions are present for greater than 250 mS. |
Action Taken When the DTC Sets
No audio is heard from the OnStar module.
Conditions for Clearing the DTC
| • | The conditions for setting the DTC are no longer present on either mono audio signal circuit. |
| • | A history DTC clears after 50 malfunction-free ignition cycles. |
Diagnostic Aids
| • | This DTC may be stored as a history DTC without affecting the operation of the module. |
| • | If stored only as a history DTC and not retrieved as a current DTC, do not replace the module. |
Reference Information
Schematic Reference
Radio/Navigation System Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Radio/Audio System Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
If this DTC is retrieved as a current DTC, replace the module that set the DTC.
