Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC B1478: Retained Accessory Power Circuit High: Description
Body Control Module (BCM) interfaces with vehicle's power distribution system through Retained Accessory Power (RAP) relay. RAP relay allows BCM to control application of power to feed circuits to sunroof and power windows. When ignition switch is in either ACC or RUN position, BCM energizes RAP relay by applying battery voltage to control circuit.
BCM turns off RAP relay when ignition switch is in START position. RAP feature therefore disables during engine cranking. When ignition switch turns from RUN or ACC to LOCK or OFF, with all of vehicle doors closed, BCM leaves RAP relay energized for 10 minutes, or until any vehicle door opens and BCM detects a ground signal in one of door ajar circuits.
DTC B1478 is set when BCM detects a short to battery in RAP relay control circuit when BCM is trying to de-energize RAP relay. Problem above must be present for more than 30 seconds.
When DTC B1478 is set, circuits powered by RAP relay remain powered at all times if RAP relay control circuit is shorted to battery voltage. BCM stores DTC B1478 in memory.
Current DTC B1478 clears and becomes a history DTC when malfunction is no longer present. History DTC B1478 clears when module ignition cycle counter reaches reset threshold, without a repeat of malfunction.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.