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 backup battery provides voltage to the communication interface module (CIM), 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 CIM detects that the back-up battery voltage has dropped below the minimum threshold value.

#### B1447

The CIM 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 CIM 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 CIM detects the voltage of the backup battery is above the minimum threshold value.

• | A current DTC B1447 will clear when the CIM detects voltage from the backup battery.

• | A history DTC clears after 50 malfunction-free ignition cycles.

### Diagnostic Aids

Important:

• | Shorting the backup battery positive voltage circuit to the backup battery ground circuit or chassis ground will activate the internal circuit protection of the backup battery, rendering the backup battery inoperable.

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

### 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

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X1 at the CIM.
2. Test for greater than 15.5 volts between terminals 13 and 14.

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

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Communication Interface Module Battery Replacement

• | Control Module References for CIM replacement, setup and programming