System Description
The body control module (BCM) controls the retained accessory power (RAP) feature. The RAP feature allows the following components to operate for 10 minutes (or until a vehicle door opens) after the ignition switch turns from RUN or ACC to LOCK or OFF:
| • | The radio |
| • | The power windows |
| • | The power sunroof, if equipped |
The BCM interfaces with the vehicle's power distribution system through the RAP relay. The RAP relay allows the BCM to control the application of power to circuit 75. Circuit 75 then powers the following circuits:
- Circuit 43: The radio
- Circuit 143: The power windows and power sunroof
When the ignition switch is in either the ACC or the RUN position, the BCM energizes the RAP relay by grounding circuit 707.
The BCM turns off the RAP relay when the ignition switch is in the START position. The RAP feature therefore disables during engine crank and bulb test.
When the ignition switch turns from RUN to LOCK or OFF with all the vehicle doors closed, the BCM leaves the RAP relay energized for 10 minutes, or until any vehicle door opens (the BCM detects a ground signal in circuit 49 or circuit 727).
The RAP feature is not available on the Century Custom model. The following modes have the RAP feature:
| • | The Century Limited |
| • | The Regal Custom |
| • | The Regal Gran Sport |
Conditions for Setting the DTC
| • | The BCM detects a short to B+ in circuit 707 when the ignition switch is in RUN and the BCM attempts to energize the RAP relay. |
| • | All conditions are present for more than 0.3 seconds. |
Action Taken When the DTC Sets
| • | The BCM stores DTC B1478 in memory. |
| • | The BCM turns off the output to the RAP relay. |
Conditions for Clearing the DTC
| • | Under all conditions, the ignition switch must be cycled from the LOCK or OFF position to the RUN position before DTC B1478 is able to change from current to history. |
| • | A short to B+ in the RAP relay circuit 707 is no longer detected by the BCM. |
| • | A history DTC B1478 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present. |
| • | Using a scan tool. |
Diagnostic Aids
| • | The following conditions may cause an intermittent malfunction to occur: |
| - | An intermittent short to B+ in circuit 707 |
| - | The RAP relay coil is shorted to B+ internally |
| - | The BCM is shorted to B+ internally |
| • | The DTC B1478 is a history DTC, the fault may be intermittent. Try to perform the tests down while moving the wires and connectors. Moving the wires and connectors may cause the |
| • | DTC P1626 will set in the Powertrain Control Module (PCM) when the ignition switch is in the Body Control module (BCM) disconnected. After you complete the BCM diagnostics and repairs, refer to Engine Controls for additional information on PCM related DTCs. |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
-
This step tests for proper vehicle usage of the RAP feature.
-
The Century Custom model is not equipped with the RAP feature. The Setup New BCM procedure permanently disables the BCM from setting again DTC B1478.
-
This step tests for a short to B+ in circuit 707.
-
This step determines whether circuit 707 is shorted to B+ or the BCM is faulty.
-
This step determines whether the malfunction is intermittent or the BCM is faulty.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the BCM Diagnostic System Check performed? | -- | Go to Step 2 | |
Is the vehicle a Century Custom model? | -- | Go to Step 3 | Go to Step 4 | |
The Century Custom model is not equipped with the retained accessory power (RAP) feature. Use the Setup New BCM Procedure in order to permanently disable DTC B1478 in the BCM. Refer to Body Control System Circuit Description . Is the repair complete? | -- | System OK | -- | |
Is the voltage less than the specified value? | 2 V | Go to Step 7 | Go to Step 5 | |
Is the voltage less than the specified value? | 2 V | Go to Step 6 | Go to Step 8 | |
Does DTC B1478 reset as a current DTC? | -- | Go to Step 9 | Go to Step 10 | |
7 | Replace the RAP relay. Is the repair complete? | -- | Go to Step 11 | -- |
8 | Repair the short to B+ in circuit 707. Is the repair complete? | -- | Go to Step 11 | -- |
9 |
Is the repair complete? | -- | Go to Step 11 | -- |
10 | The malfunction is not present. Refer to Diagnostic Aids for additional information regarding DTC B1478. Is the repair complete? | -- | Go to Step 11 | -- |
11 |
Are any current BCM DTCs set? | -- | System OK |
