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
- Replace Backup Power Source

DTC B1447
- Backup Power Source

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

B1446
* Ignition is in the RUN or ACC position.
* System voltage is between 9.5 and 15.5 volts.
* DTC B1447 is not set.

B1447
* Ignition is in the RUN or ACC position.
* System voltage is between 9.5 and 15.5 volts.
* The above conditions are present for greater than 10 seconds.

Conditions for Setting the DTC

B1446

The VCIM detects that the back-up battery voltage has dropped below the minimum threshold value.

B1447

The VCIM detects no voltage from the back-up battery.

Action Taken When the DTC Sets

B1446

The OnStar(R) status LED turns red.

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

* A current DTC B1446 will clear when the VCIM detects the voltage of the back-up battery is above the minimum threshold value.
* A current DTC B1447 will clear when the VCIM detects voltage from the back-up battery.
* A history DTC clears after 50 malfunction-free ignition cycles.

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 harness connector X1 at the VCIM.
2. Using a DMM, test for greater than 15.5 volts between terminals 13 and 14.

• If less than specified voltage, test the battery backup supply voltage circuit and battery backup low reference circuit for an open/high resistance or a short to ground. If the circuits test normal, replace the BUB.

3. 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