GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 Classic 🢒 DTC 🢒 DTC B2577

Circuit Description

The body control module (BCM) turns on the automatic lighting control (ALC) headlamp relay when the ambient light sensor senses a dark condition. Battery voltage is supplied to the relay at all times through the LH HDLP fuse. The BCM grounds the ALC headlamp relay control circuit in order to activate the relay.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2577 Headlamp Control Circuit Low

Conditions for Running the DTC
    • The ignition switch is in the ON position.
    • The ambient light sensor senses a light condition, ALC headlamps OFF.

Conditions for Setting the DTC

Either of the following conditions will set this DTC:

    • The ALC headlamp relay control circuit is open for 5 seconds.
    • The ALC headlamp relay control circuit is shorted to ground for 5 seconds.

Action Taken When the DTC Sets
    • The SERVICE indicator will illuminate.
    • The check gages chime sounds.

Conditions for Clearing the DTC
    • The conditions for setting the DTC are no longer present.
    • A history DTC clears after 100 malfunction free ignition cycles.
    • The BCM receives the clear code command from the scan tool.

Diagnostic Aids
    • If the ALC headlamp relay control circuit is open, the ALC headlamps will be inoperative.
    • In the ALC headlamp relay control circuit is shorted to ground, the ALC headlamps will be always on.
    • If the DTC is a history DTC, the problem may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

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

  2. Tests for voltage at the coil side of the ALC headlamp relay. The LH HDLP fuse supplies power to the coil side of the ALC headlamp relay.

    3.

  3. Verifies that the body control module is providing ground to the ALC headlamp relay.

    4.

  4. Tests if ground is constantly being applied to the ALC 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 Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the automatic lighting control (ALC) headlamp relay ON and OFF.

Does the ALC headlamp 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 ALC headlamp relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the coil side battery positive voltage circuit of the ALC headlamp relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between the control circuit of the ALC headlamp relay and the coil side battery positive voltage circuit of the ALC headlamp relay.
  2. With a scan tool, command the ALC 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 control circuit of the ALC headlamp relay for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the control circuit of the ALC 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 13

Go to Step 9

8

Inspect for poor connections at the ALC 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 13

Go to Step 11

9

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 13

Go to Step 12

10

Repair the coil side battery positive voltage circuit of the ALC headlamp relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

Replace the ALC headlamp relay.

Did you complete the replacement?

Go to Step 13

--

12

Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming .

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