GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Blazer - 4WD - RHD 🢒 DTC 🢒 DTC B1477 or B1478

DTC B1477 or B1478 with relay

Circuit Description

The retained accessory power (RAP) function allows selected vehicle functions to operate for 10 minutes after the ignition switch is turned OFF. The 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.

Conditions for Running the DTCs B1477 and B1478
    • 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 RAP DTCs B1477 and B1478
    • When the BCM does not detect battery voltage on the RAP relay control circuit with the RAP relay commanded ON B1477 will set.
    • When the BCM detects battery voltage on the RAP relay control circuit with the ignition in the RUN position B1478 will set.
    • The system voltage must be between 9.0-16.0 volts.
    • The above conditions must be met for 0.5 seconds.

Action Taken When the DTCs Set
    • Any function that is RAP enabled will not operate
    • Refer to Retained Accessory Power (RAP) Schematics that are RAP enabled.

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

Perform a visual inspection of the wiring, the terminals and the connectors.

Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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

1

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

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. With a scan tool, command the RAP relay ON and OFF.

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

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Remove the RAP relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the non control circuit of the RAP relay for voltage or ground as required by the schematic.

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 and the battery positive voltage circuit of the RAP relay.
  2. With a scan tool, command the RAP relay ON and OFF .

Are the circuits functional?

Go to Step 6

Go to Step 5

5

Test the control circuit of the RAP relay for a:

    • Short to ground
    • Short to battery positive voltage
    • 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 non control 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.

Did you complete the replacement?

Go to Step 11

--

10

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

Did you complete the replacement?

Go to Step 11

--

11
  1. Use the scan tool in order to clear the DTCs .
  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