B1478

DTC B1478

CIRCUIT DESCRIPTION
The retained accessory power (RAP) function allows selected vehicle functions to operate for 10 minutes after the ignition switch is turned OFF. The BCM monitors the ignition switch position, the door jamb switches and the voltage on the RAP relay control circuit . The BCM will command the RAP relay ON by grounding the RAP relay control circuit when all the doors are CLOSED and the ignition switch is switched to the OFF position.

CONDITIONS FOR RUNNING THE DTCS B1477 AND B1478
- The system voltage must be between 9.0-16.0 volts.
- The doors must be closed.
- The ignition switch must be cycled from ON to OFF.

CONDITIONS FOR SETTING RAP DTCS B1477 AND B1478
- When the BCM does not detect battery voltage on the RAP relay control circuit with the RAP relay commanded ON B1477 will set.
- When the BCM detects battery voltage on the RAP relay control circuit with the ignition in the RUN position B1478 will set.
- The system voltage must be between 9.0-16.0 volts.
- The above conditions must be met for 0.5 seconds.

ACTION TAKEN WHEN THE DTCS SET
- Any function that is RAP enabled will not operate
- Refer to Retained Accessory Power (RAP) Schematics that are RAP enabled.

CONDITIONS FOR CLEARING THE DTC
- A current DTC clears when the malfunction is no longer present.
- A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DIAGNOSTIC AIDS
Perform a visual inspection of the wiring, the terminals and the connectors.

TEST DESCRIPTION

Steps 1-6:

Steps 7-11:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the RAP relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. Tests for voltage at the coil side of the RAP relay. The RAP fuse supplies power to the coil side of the RAP relay.
4. Verifies that the BCM is providing ground to the RAP relay.
5. Tests the control circuit side of the RAP relay for faults that cause both B1477 and B1478 RAP DTCs.
10. After replacement of the BCM you must calibrate the new module for proper operation.