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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2007 🢒 Rendezvous - FWD 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC B1478

Circuit Description

The body control module (BCM) controls the retained accessory power (RAP) feature. The RAP feature allows the following components to operate for 10 minutes, or until a vehicle door opens, after the ignition switch turns from RUN or ACC to LOCK:

    • The radio
    • The power windows
    • The power sunroof, if equipped

The BCM interfaces with the vehicle's power distribution system through the RAP relay. The RAP relay allows the BCM to control the application of power to the RAP controlled feed circuit. When the ignition switch is in either the ACC or the RUN position, the BCM energizes the RAP relay by powering the RAP relay control feed circuit.

The BCM turns OFF the RAP relay when the ignition switch is in the START position. The RAP feature therefore disables during engine crank and bulb test.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1478 Retained Accessory Power Circuit High

Conditions for Running the DTC

The BCM must not be commanding the RAP relay to energize after the RAP feature 10 minute time-out or after a door has been opened during the 10 minute time-out.

Conditions for Setting the DTC
    • The BCM detects a short to battery or open in the RAP relay control feed circuit when it is not trying to energize the RAP relay.
    • The condition above must be present for more than 0.3 seconds.

Action Taken When the DTC Sets

The BCM stores DTC B1478 in memory.

Conditions for Clearing the DTC
    • A current DTC B1478 will clear if the short to battery or open in the RAP relay control feed circuit is no longer detected by the BCM.
    • A history DTC B1478 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

Diagnostic Aids
    • If the DTC B1478 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .
    • The following conditions may cause an intermittent malfunction to occur:
       - An intermittent short to battery or open in the RAP relay control feed circuit
       - The RAP relay coil is intermittently shorted to battery or open internally.
       - The BCM is intermittently shorted to battery or open internally.

Test Description

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

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

    2.

  2. This step verifies that the BCM is providing voltage to the RAP relay.

    3.

  3. This step tests for an open in the ground circuit to the RAP relay.

    4.

  4. This step tests if voltage is constantly being applied to the RAP relay.

Step

Action

Yes

No

Schematic Reference: Data Communication Schematics

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the retained accessory power (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. Disconnect the RAP relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the control circuit of the RAP relay with a test lamp connected to a good ground.
  5. With a scan tool, command the RAP relay ON and OFF.

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

Go to Step 4

Go to Step 5

4

  1. Connect a test lamp between the control circuit of the RAP relay and the ground circuit of the RAP relay.
  2. With a scan tool, command the RAP relay ON and OFF.

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

Go to Step 7

Go to Step 9

5

Does the test lamp remain illuminated with each command?

Go to Step 6

Go to Step 7

6

Test the control circuit of the RAP relay for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 8

7

Inspect for poor connections at the RAP relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 10

8

Inspect for poor connections at the console electrical center connector to the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 11

9

Repair the ground circuit of the RAP relay. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 12

--

10

Replace the RAP relay.

Did you complete the replacement?

Go to Step 12

--

11

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

Did you complete the replacement?

Go to Step 12

--

12
  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