GM Service Manual Online
For 1990-2009 cars only

Circuit Description

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

Conditions for Running the DTC

The BCM must not be commanding the headlamp relay to energize.

Conditions for Setting the DTC

    • The BCM detects a short to ground or open in the headlamp relay coil control circuit when the BCM is not trying 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 B2577 in memory.

Conditions for Clearing the DTC

    • A current DTC B2577 will clear if the BCM no longer detect a short to ground or open in the headlamp relay coil control circuit.
    • A history DTC B2577 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

Diagnostic Aids

    • If the DTC B2577 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 open in the headlamp relay control circuit.
       - The headlamp relay coil is intermittently shorted to ground or open internally.
       - The BCM is intermittently shorted to ground or open internally.

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. Using a test lamp connected to ground, probe the headlamp relay coil side battery positive voltage circuit.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between the headlamp relay coil side battery positive voltage circuit and the headlamp relay control circuit.
  2. With a scan tool, command the headlamp relay ON and OFF.

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

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

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

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

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

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

Inspect for poor connections at the headlamp relay. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

9

Inspect for poor connections at the harness connector of the body control module. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Replace the LH Accessory Wiring Junction Block. Refer to Instrument Panel Electrical Center or Junction Block Replacement - Left Side in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

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

Did you complete the replacement?

Go to Step 13

--

12

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

Replace the body control module. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 13

--

13

  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