Diagnostic Instructions
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 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. |
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 back-up battery is above the minimum threshold value. |
| • | A current DTC B1447 will clear when the CIM 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 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 BUB 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
Circuit/System Testing
- Ignition OFF, disconnect the harness connector X1 at the CIM.
- 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 BUB. |
- If all circuits test normal, replace the CIM.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
