GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Astro - 2WD 🢒 DTC 🢒 DTC B1477 or B1478

Circuit Description

The retained accessory power (RAP) function allows selected vehicle functions to operate after the ignition switch is turned OFF. The body control module (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. The BCM monitors voltage on the RAP relay control circuit. If the BCM detects that the RAP relay control circuit is open or shorted, DTC B1477 or B1478 will set.

DTC Descriptors

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 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 the DTC
    • If the BCM detects low voltage on the RAP relay control circuit when the RAP relay is commanded OFF, DTC B1477 will set.
    • If the BCM detects battery voltage on the RAP relay control circuit when the RAP relay is commanded ON, DTC B1478 will set.
    • One of the above conditions is met for 0.5 seconds.

Action Taken When the DTCs Set

The RAP function will not operate. Refer to Retained Accessory Power (RAP) Schematics for the modules that are powered by the RAP relay.

Conditions for Clearing the DTC
    • A current DTC clears when the malfunction is no longer present.
    • A history DTC clears when the ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Listen for an audible click when the RAP relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. Tests for voltage at the coil side of the RAP relay. The RAP fuse supplies power to the coil side of the RAP relay.

    3.

  3. Verifies that the BCM is providing ground to the RAP relay.

    4.

  4. Tests the control circuit side of the RAP relay for faults that cause both B1477 and B1478 RAP DTCs.

    5.

  5. After replacement of the BCM you must calibrate the new module for proper operation.

Step

Action

Yes

No

Schematic Reference: Retained Accessory Power (RAP) Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

1

Did you perform the Diagnostic System Check - Retained Accessory Power?

Go to Step 2

Go to Diagnostic System Check - Retained Accessory Power

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Command the RAP relay ON and OFF with a scan tool.

Does the RAP relay turn ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Remove the RAP relay. Refer to Relay Replacement in Wiring Systems.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the battery positive voltage circuit of the RAP relay and a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 8

4

  1. Connect a test lamp between the RAP relay control circuit of the RAP relay coil and the battery positive voltage circuit of the RAP relay coil.
  2. Command the RAP relay ON and OFF with a scan tool.

Does the test lamp illuminate with each command?

Go to Step 6

Go to Step 5

5

Test the control circuit of the RAP relay for following:

    • Short to ground
    • Short to battery positive voltage
    • An open circuit

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 7

6

Inspect for poor connections and terminal damage at the RAP relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 9

7

Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 10

8

Repair the battery positive voltage circuit of the RAP relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 11

--

9

Replace the RAP relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 11

--

10

Important: Perform the BCM setup procedure if required.

Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 11

--

11
  1. Clear the DTCs with the scan tool.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK