B1478

DTC B1478

CIRCUIT DESCRIPTION
The body control module (BCM) interfaces with the vehicles power distribution system through the retained accessory power (RAP) relay. The RAP relay allows the BCM to control the application of power to the feed circuits to the sunroof and the power windows. When the ignition switch is in either the ACC or the RUN position, the BCM energizes the RAP relay by applying battery voltage to the control circuit.

The BCM turns OFF the RAP relay when the ignition switch is in the START position. The RAP feature, therefore, disables during engine cranking.

When the ignition switch turns from ON or ACC to LOCK or OFF, with all of the vehicle doors closed, the BCM leaves the RAP relay energized for 10 minutes, or until any vehicle door opens and the BCM detects a ground signal in 1 of the door ajar circuits.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC B1478 Retained Accessory Power Circuit High

CONDITIONS FOR RUNNING THE DTC
The BCM must be commanding the RAP relay to energize.

CONDITIONS FOR SETTING THE DTC
- The BCM detects a short to battery in the RAP relay control circuit when the BCM is trying to de-energize the RAP relay.
- The condition above must be present for more than 300 milliseconds.

ACTION TAKEN WHEN THE DTC SETS
- The circuits powered by the RAP relay remain powered at all times, if the RAP relay control circuit is shorted to battery voltage.
- The BCM stores DTC B1478 in memory.

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.

TEST DESCRIPTION

Steps 1 - 13:

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. Test for voltage at the coil side of the RAP Relay.
4. This step verifies that the BCM is providing ground to the RAP relay.
5. This step tests if ground is constantly being applied to the RAP relay.