Circuit Description
The vehicle communication interface module (VCIM) detects the Back-up Battery (BUB) is no longer connected to the VCIM.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B1447 Back-up Power Source
Conditions for Running the DTC
| • | The ignition must be in the RUN or ACC position. |
| • | The system voltage is at least 9.5 volts and no more than 15.5 volts. |
| • | All the above conditions are present for greater than 10 seconds |
Conditions for Setting the DTC
The VCIM detects no voltage from the back-up battery
Action Taken When the DTC Sets
| • | The VCIM will be unable to place a call in the event of a main battery disconnect during a collision event. |
| • | The OnStar® status LED turns RED. |
Conditions for Clearing the MIL/DTC
| • | The VCIM detects voltage from the back-up battery. |
| • | A history DTC clears after 50 malfunction-free ignition cycles. |
| • | The VCIM receives the clear DTC command from the scan tool. |
Diagnostic Aids
DTC B1447 may set if the VCIM has been incorrectly disconnected or services. When disconnecting the VCIM, disconnect the harness connector C1 at the VCIM prior to disconnecting any other harness connectors. This will ensure the BUB is preserved when voltage is removed from the VCIM.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: OnStar Schematics Connector End View Reference: Cellular Communication Connector End Views | ||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | ||||||
2 |
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 Back up Battery (BUB), rendering the BUB inoperable.
Does the voltage measure greater than the specified value? | 16.0 V | Go to Step 3 | Go to Step 5 | ||||
3 | Inspect the following circuits for an open or short to ground:
Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 4 | ||||
4 | Inspect for poor connections at the harness connector of the vehicle communication interface module (VCIM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6 | ||||
5 | Replace the BUB. Refer to Communication Interface Module Battery Replacement . Did you complete the replacement? | -- | Go to Step 7 | -- | ||||
6 | Replace the VCIM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 7 | -- | ||||
7 |
Does the DTC reset? | -- | Go to Step 2 | System OK | ||||
