For 1990-2009 cars

### 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 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 (VVCIM), allowing the VVCIM 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 9.5-15.5 volts.

• | DTC B1447 is not set.

#### B1447

• | Ignition is in the RUN or ACC position.

• | System voltage is between 9.5-15.5 volts.

• | The above conditions are present for greater than 10 seconds.

### Conditions for Setting the DTC

#### B1446

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

#### B1447

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

### Action Taken When the DTC Sets

#### B1446

The OnStar® status LED turns red.

#### B1447

• | The OnStar® status LED turns red.

• | The VVCIM 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 VVCIM detects the voltage of the back-up battery is above the minimum threshold value.

• | A current DTC B1447 will clear when the VVCIM 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 VVCIM has been incorrectly disconnected or serviced. When disconnecting the VVCIM, disconnect the X1 harness connector at the VVCIM prior to disconnecting any other harness connectors. This will ensure the BUB is preserved when voltage is removed from the VVCIM.

### Reference Information

#### Schematic Reference

OnStar Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

OnStar Description and Operation

#### Electrical Information Reference

• | Testing for Intermittent Conditions and Poor Connections

• | Circuit Testing

• | Wiring Repairs

• | Connector Repairs

### Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the VVCIM.
2. Test for greater than 15.5 volts between the BUB B+ circuit terminal 14 and the BUB ground circuit terminal 13.

⇒ | If not within than specified range, test the BUB B+ circuit and BUB ground circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the BUB.

3. If all circuits test normal, replace the VVCIM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for VVCIM replacement, setup and programming