GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC B1478

Circuit Description

The BCM interfaces with the vehicle's power distribution system through the RAP#1 relay. The RAP#1 relay allows the BCM to control the application of power to the feed accessory circuits.

When the ignition switch turns from ON/RUN to LOCK or OFF, with all of the vehicle doors closed, the BCM leaves the RAP#1 relay energized for 20 minutes, or until any vehicle door opens and the BCM detects a ground signal in one of the door ajar circuits.

Conditions for Running the DTC

The BCM must be commanding the RAP#1 relay to energize.

Conditions for Setting the DTC
    • The BCM detects a short to battery in the RAP#1 relay control circuit when the BCM is trying to energize the RAP relay.
    • The condition above must be present for more than 300 milliseconds.

Action Taken When the DTC Sets
    • The RAP#1 relay powered functions will not operate.
    • The BCM stores DTC B1478 in memory.

Conditions for Clearing the DTC
    • A current DTC B1478 will clear if the short to battery in the RAP#1 relay control circuit is no longer detected by the BCM when the RAP#1 relay is commanded to energize.
    • A history DTC B1478 will clear after the module 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#1 relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

  2. This step verifies that the Body Control Module (BCM) is providing ground to the RAP#1 relay.

Step

Action

Yes

No

1

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

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#1 Relay ON and OFF.

Does the RAP#1 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. Disconnect the RAP#1 relay.
  3. Connect a test lamp between the RAP#1 relay control circuit and the RAP#1 relay coil supply voltage circuit at the RAP#1 relay.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, command the RAP#1 relay ON and OFF .

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

Go to Step 5

Go to Step 4

4

Test the RAP#1 relay control circuit 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 9

Go to Step 6

5

Inspect for poor connections at the RAP#1 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 9

Go to Step 7

6

Inspect for poor connections at the harness connector of the body control module (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 9

Go to Step 8

7

Replace the RAP#1 relay.

Did you complete the repair?

Go to Step 9

--

8

Important: Perform the set up procedure for the BCM. Refer to Body Control Module (BCM) Programming/RPO Configuration in Body Control System.

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

Did you complete the repair?

Go to Step 9

--

9
  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