GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 Savana 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 DTC B1477 or B1478

Circuit Description

The body control module (BCM) interfaces with the vehicle power distribution system through the WND RAP relay. The WND RAP relay allows the BCM to control the application of power to the feed circuits of the power windows. When the ignition switch is in either the ACC or the ON position, the BCM energizes the WND RAP relay by providing B+ to the WND RAP relay control circuit.

The BCM turns OFF the WND RAP relay when the ignition switch is in the START position.

When the ignition switch turns from ON or ACC to OFF, with all of the vehicle doors closed, the BCM leaves the WND RAP relay energized for 10 minutes, or until any vehicle door opens.

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 9-16 volts.

Conditions for Setting the DTC

DTC B1477

    • The BCM detects a short to ground in the WND RAP relay control circuit when the BCM is trying to energize the WND RAP relay.
    • The condition above must be present for more than 1 second.

DTC B1478

    • The BCM detects a short to battery or an open in the WND RAP relay control circuit when the WND RAP relay is not energized.
    • The condition above must be present for more than 1 second.

Action Taken When the DTC Sets

DTC B1477

    • The BCM stores DTC B1477 in memory.
    • The circuits powered by the WND RAP relay will not operate.

DTC B1478

    • The BCM stores DTC B1478 in memory.
    • The circuits powered by the WND RAP relay remain powered at all times if the relay control circuit is shorted to battery.
    • The circuits powered by the WND RAP relay will never be powered if the relay control circuit is open.

Conditions for Clearing the DTC
    • A current DTC clears when the malfunction is no longer present.
    • A history DTC clears when the ignition has been cycled 100 times, without a repeat of the malfunction.

Diagnostic Aids

If the DTC B1477 or B1478 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

The following conditions may cause an intermittent malfunction to occur:

    • An intermittent short to ground or to battery in the WND RAP relay control circuit
    • The WND RAP relay coil is shorted to ground or to battery internally.
    • The BCM is shorted to ground or to battery internally.

Test Description

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

  1. During the WND RAP relay operation, listen for an audible click. Command the ON and the OFF states. Repeat the commands as necessary.

    2.

  2. This step verifies whether the WND RAP relay has a defect.

    3.

  3. This step tests the ground circuit of the WND RAP relay.

  4. This step tests the control circuit of the WND RAP relay.

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 - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

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

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

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the WND RAP relay.
  3. Connect a test lamp between the relay coil circuits of the WND RAP relay.
  4. Command the RAP relay ON and OFF, with a scan tool.

Does the test lamp turn ON and OFF with each command?

Go to Step 6

Go to Step 4

4

Test the ground circuit of the WND RAP relay coil for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 5

5

  1. Disconnect the body control module (BCM).
  2. Test the WND RAP relay control circuit for a short to voltage, a ground, or an open.
  3. Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 7

6

Inspect for poor connections at the WND 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 10

Go to Step 8

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 10

Go to Step 9

8

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

Did you complete the replacement?

Go to Step 10

--

9

Replace the BCM . Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 10

--

10
  1. Reconnect all previously disconnected modules.
  2. Use the scan tool in order to clear the DTCs.
  3. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

Go to Step 2

System OK