GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2001 🢒 Intrigue 🢒 Body and Accessories 🢒 Lighting Systems 🢒 DTC B2578

Circuit Description

The body control module (BCM) controls the headlamp relay. The BCM grounds the headlamp relay control circuit, which energizes the headlamp relay.

Conditions for Running the DTC

The BCM must command the headlamp relay to energize.

Conditions for Setting the DTC
    • The BCM detects a short to battery positive voltage in the headlamp relay control circuit when the BCM tries to energize the headlamp relay.
    • The condition above must be present for more than 0.3 seconds.

Action Taken When the DTC Sets

The BCM stores DTC B2578 in memory.

Conditions for Clearing the DTC
    • A current DTC B2578 will clear if the BCM no longer detects a short to battery in the headlamp relay control circuit, after the ignition is cycled.
    • A history DTC B2578 will clear after 100 consecutive ignition cycles if the condition for the condition is no longer present.
    • The BCM receives the Clear Code command from the scan tool.

Diagnostic Aids
    • If the DTC B2578 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 condition to occur:
       - An intermittent short to battery in the headlamp relay control circuit.
       - The headlamp relay coil is intermittently shorted to battery.
       - The BCM is intermittently shorted to battery.

Test Description

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

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

    2.

  2. Verifies that the BCM is providing ground to the headlamp relay control circuit. Indicating a short to voltage internal to the headlamp relay.

    3.

  3. Test for a short to voltage on the headlamp relay control circuit.

Step

Action

Yes

No

Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics

1

Did you perform the Lighting System Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the headlamp relay ON and OFF.

Does the headlamp 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 headlamp relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between battery positive voltage supply circuit and the headlamp relay control circuit of the headlamp relay.
  5. With a scan tool, command the headlamp relay ON and OFF .

Does the test lamp illuminate?

Go to Step 5

Go to Step 4

4

Test the headlamp relay control circuit for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 7

Go to Step 6

5

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

Did you complete the replacement?

Go to Step 7

--

6

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 replacement?

Go to Step 7

--

7
  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 set again?

Go to Step 2

System OK