B1446

DTC B1446 or B1447

Diagnostic Instructions

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

DTC Descriptors

DTC B1446 03
- Replace Backup Power Source Voltage Below Minimum Threshold

DTC B1447 04
- Backup Power Source Open Circuit

DTC B1447 07
- Backup Power Source Component Protection Timeout Voltage Above Threshold

Circuit/System Description

The Back-up Battery (BUB) provides voltage to the vehicle communication interface module (VCIM), to be able to successfully place a call in the event of a main battery disconnect during a collision event.

Conditions for Running the DTC

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

Conditions for Setting the DTC

DTC B1446

DTC B1446 will set when the VCIM detects a short to ground in the battery backup voltage supply circuit or the backup battery voltage has dropped below the minimum threshold value.

DTC B1447

DTC B1447 will set when the VCIM detects an open/high resistance in the battery backup voltage supply circuit, a short to voltage or an open/high resistance in the battery backup low reference circuit, or no voltage from the back-up battery.

Action Taken When the DTC Sets

DTC B1446

The OnStar(R) status LED turns red.

DTC B1447
* The OnStar(R) status LED turns red.
* The VCIM will be unable to place a call in the event of a main battery disconnect during a collision event.

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.

Diagnostic Aids

Important:
* Shorting the back-up battery positive voltage circuit to the back-up battery ground circuit or chassis ground will activate the internal circuit protection of the BUB, rendering the BUB inoperable.

* DTC B1447 may set if the VCIM has been incorrectly disconnected or serviced. When disconnecting the VCIM, disconnect the harness connector X1 at the VCIM prior to disconnecting any other harness connectors. This will ensure the BUB is preserved when voltage is removed from the VCIM.

Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the VCIM.
2. Test for 15.5 volts or greater between the battery backup supply voltage circuit terminal 14 and ground.

^ If less than specified range, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the backup battery.

3. Verify that a test lamp illuminates between the battery backup supply voltage circuit terminal 14 and the backup battery low reference circuit terminal 13

^ If the test lamp does not illuminate, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the backup battery.

4. If all circuits test normal, replace the VCIM.

Repair Instructions

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

* Communication Interface Module Battery Replacement