GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 Equinox 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC B2577

Circuit Description

The body control module (BCM) energizes the headlamp relay when the ambient light sensor senses a dark condition. Battery positive voltage is supplied to the headlamp relay when the ignition is in the RUN position. The BCM grounds the 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 RUN position.
    • The ambient light sensor senses a light condition, automatic lamp control (ALC) headlamps OFF.

Conditions for Setting the DTC

Either of the following conditions will set this DTC:

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

Action Taken When the DTC Sets

The headlamps will remain illuminated or will not illuminate in ALC mode.

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

Diagnostic Aids
    • If the headlamp relay control circuit is open, the ALC headlamps will be inoperative.
    • In the 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 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 headlamp relay. The ignition switch supplies battery positive voltage to the coil side of the headlamp relay.

    3.

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

    4.

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

Step

Action

Yes

No

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

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 headlamp relay ON and OFF.

Does the 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 headlamp relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the coil side battery positive voltage circuit of the 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 headlamp relay and the coil side battery positive voltage circuit of the 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 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 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 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 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 headlamp relay. Refer to Wiring Repairs 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

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