GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2003 🢒 Century 🢒 DTC 🢒 DTC B2577

Circuit Description

The Body Control Module (BCM) controls the automatic headlamp relay through the headlamp relay control circuit. The BCM grounds the automatic headlamp relay control circuit energizing 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 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 detects a short to ground or open in the automatic headlamp relay control circuit.
    • A history DTC B2577 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • The BCM receives a clear code command from the scan tool.

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 automatic headlamp relay control circuit.
       - The headlamp relay coil is intermittently shorted to ground or open.
       - The BCM is intermittently shorted to ground or open.

Test Description

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

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

    2.

  2. Tests for voltage at the coil side feed of the automatic headlamp relay. The LP Park fuse supplies power to the coil side feed of the automatic headlamp relay.

    3.

  3. Verifies that the BCM is providing ground to the automatic headlamp relay.

    4.

  4. Tests if ground is constantly being applied to the automatic headlamp relay.

Step

Action

Yes

No

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

Connector End View Reference: Master Electrical Component List in Wiring Systems

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

Check the LP PARK fuse for an open.

Is the LP PARK fuse open?

Go to Step 12

Go to Step 4

4

  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 coil side supply circuit of the automatic headlamp relay.

Does the test lamp illuminate?

Go to Step 5

Go to Step 11

5

  1. Connect a test lamp between the control circuit of the automatic headlamp relay and the coil side supply circuit of the automatic headlamp relay.
  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 9

Go to Step 6

6

Does the test lamp remain illuminated with each command?

Go to Step 8

Go to Step 7

7

Test the control circuit of the automatic headlamp relay for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 10

8

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

Did you find and correct the condition?

Go to Step 15

Go to Step 10

9

Inspect for poor connections at the automatic headlamp 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 15

Go to Step 13

10

Inspect for poor connections at the harness connector of the Body Control Module. 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 15

Go to Step 14

11

Repair a poor connection or an open in the automatic headlamp relay coil supply circuit. Refer to Circuit Testing and Wiring Repairs in Wiring System.

Did you complete the repair?

Go to Step 15

--

12

Repair a short to ground in one of the LP PARK fuse battery positive supply circuits. Refer to Circuit Testing and Wiring Repairs in Wiring System.

Did you complete the repair?

Go to Step 15

--

13

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

Did you complete the replacement?

Go to Step 15

--

14

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

Did you complete the replacement?

Go to Step 15

--

15
  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