B1478
DTC B1477 or B1478
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
DTC Descriptors
DTC B1477
- Retained Accessory Power Control Circuit Low
DTC B1478
- Retained Accessory Power Control Circuit High
Diagnostic Fault Information
Circuit/System Description
The body control module (BCM) controls the RAP/ACCY relay. The relay allows the BCM to control the application of power to the feed circuits of multiple subsystems and components. When the ignition switch is in either the ACC or the ON position, the BCM energizes the relay by providing ground to the RAP relay coil control circuit. The BCM also energizes the relay for a specific time after the ignition key is removed providing a set of specific conditions are met. Refer to retained accessory power (RAP) description and operation for more information on RAP.
Conditions for Running the DTC
Battery voltage is 9-16 volts.
Conditions for Setting the DTC
B1477
* The BCM detects an open or a short to ground in the RAP relay coil control circuit when the RAP/ACCY relay is not energized.
* The condition above must be present for more than 1 second.
B1478
* The BCM detects a short to voltage in the RAP relay coil control circuit when the BCM is trying to energize the RAP/ACCY relay.
* The condition above must be present for more than 1 second.
Action Taken when the DTC Sets
* The BCM stores the DTC in memory.
* The devices powered by the relay will not operate if the relay control circuit is open or shorted to B+.
* The devices powered by the relay will be able to be operated beyond the time limit if the relay control circuit is shorted to ground.
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
* An open or short to ground between the fuses and subsystems will only effect the individual subsystem. Refer to the specific system for diagnostics.
* A short to voltage will backfeed through all fuses and effect all subsystems connected to the controlled circuit of the RAP/ACCY relay
Reference Information
Schematic Reference
Power Moding Schematics (Retained Accessory Power (RAP))
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Retained Accessory Power (RAP) Description and Operation (Retained Accessory Power (RAP) Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Testing
1. Ignition OFF, disconnect the RAP/ACCY relay.
2. Connect a test lamp between the relay coil control circuit terminal 86 and B+.
3. With the driver door open, cycle the ignition ON and OFF. The test lamp should turn ON and OFF when changing ignition switch positions.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the control circuit for a short to voltage or open/high resistance. If the circuit tests normal, replace the BCM.
4. If the test lamp illuminates normal, test or replace the RAP/ACCY relay.
Component Testing
Rap Relay Test
1. Ignition OFF, disconnect the RAP relay.
2. Test for 70-110 ohms between terminals 85 and 86.
• If the resistance is not within the specified range, replace the relay.
3. Test for infinite resistance between the following terminals:
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If less specified, replace the relay.
4. Install a 20-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 5 ohms of resistance between terminals 30 and 87.
• If greater than specified, replace the relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming