B1478

DTC B1477 or B1478

CIRCUIT DESCRIPTION
The body control module (BCM) controls the retained accessory power (RAP) relay. The RAP relay allows the BCM to control the application of power to the feed circuits of the windshield wipers and power windows. When the ignition switch is in either the ACC or the ON position, the BCM energizes the RAP relay by providing ground to the RAP relay control circuit.

When the ignition switch turns from ON or ACC to OFF, with all of the vehicle doors closed, the BCM leaves the RAP relay energized for 10 minutes, or until any vehicle door opens.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTCs:
- DTC B1477 Retained Accessory Power Circuit Low
- DTC B1478 Retained Accessory Power Circuit High

CONDITIONS FOR RUNNING THE DTC
The system voltage is between 9-16 volts.

CONDITIONS FOR SETTING THE DTC

DTC B1477
- The BCM detects an open or a short to ground in the RAP relay control circuit when the RAP relay is not energized.
- The condition above must be present for more than 1 second.

DTC B1478
- The BCM detects a short to voltage in the RAP relay control circuit when the BCM is trying to energize the RAP relay.
- The condition above must be present for more than 1 second.

ACTION TAKEN WHEN THE DTC SETS

DTC B1477
- The BCM stores DTC B1477 in memory.
- The windshield wipers and power windows will not operate if the relay control circuit is open.
- The windshield wipers and power windows will operate at all times if the relay control circuit is shorted to ground.

DTC B1478
- The BCM stores DTC B1478 in memory.
- The windshield wipers and power windows will not operate.

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
If the DTC B1477 or B1478 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics

The following conditions may cause an intermittent malfunction to occur:
- An intermittent short to ground or to battery in the RAP relay control circuit.
- The RAP relay coil is shorted to ground or to battery internally.
- The BCM is shorted to ground or to battery internally.

TEST DESCRIPTION

Step 1 - Step 10:

The numbers below refer to the step numbers on the diagnostic table.
2. During the RAP relay operation, listen for an audible click. Command the ON and the OFF states. Repeat the commands as necessary.
3. Verifies whether the RAP relay has a defect.
4. Tests the control circuit of the RAP relay.
5. Tests the coil supply voltage circuit of the RAP relay.