GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Classic - 4WD 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC B2575

Circuit Description

When the body control module (BCM) senses a request for low beam headlamp illumination, the BCM sends a ground signal to the low beam headlamp relay through the headlamp low beam relay control circuit. The headlamp low beam relay will apply voltage to illuminate the headlamps.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2575 (Left or generic) Headlamp Control Circuit

Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

Conditions for Setting the DTC
    • When the BCM receives a command to illuminate the low beam headlamps and the headlamp low beam relay control circuit is open or shorted to voltage
    • When the BCM does not receive a command to illuminate the low beam headlamps and the headlamp low beam relay control circuit is shorted to ground
    • When the low beam relay coil side is open or the battery positive voltage to the low beam relay is open

Action Taken When the DTC Sets

The low beam headlamps will not operate or will remain always on.

Conditions for Clearing the MIL/DTC
    • This DTC will clear on current status after the condition for setting the fault is corrected.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • History and current DTCs can be cleared using a scan tool.

Test Description

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

  1. This step tests for voltage at the voltage supply side of the headlamp low beam relay.

    2.

  2. This step verifies that the BCM is providing ground to the headlamp low beam relay.

    3.

  3. This step tests if ground is constantly being applied to the headlamp low beam relay.

    4.

  4. This step tests if there is opposing voltage present or an open headlamp low beam relay control circuit, including the relay coil side.

    5.

  5. After replacement of the BCM you must calibrate the new module for proper operation.

Step

Action

Yes

No

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

Connector End View Reference: Lighting Systems Connector End Views or Data Communication Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Turn ON the ignition, with the engine OFF.
  2. Place the headlamp switch in the ON position.
  3. Place the headlamp dimmer switch in the low beam position.
  4. Place the headlamp switch in the OFF position.

Do the low beam headlamps operate as expected?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the headlamp low beam relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the control circuit of the headlamp low beam relay and 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 low beam relay and the battery positive voltage circuit of the headlamp low beam relay.
  2. While observing the test lamp, place the headlamp switch in the ON position, and then the OFF position.

Does the test lamp turn ON and OFF with each cycle of the switch?

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each cycle of the switch?

Go to Step 7

Go to Step 6

6

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

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the control circuit of the headlamp low beam relay for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

Inspect for poor connections at the headlamp low beam relay. Refer to Circuit Testing and Wiring Repairs .

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 Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair the battery positive voltage circuit of the headlamp low beam relay. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 13

--

11

Replace the headlamp low beam relay. Refer to Relay Replacement .

Did you complete the replacement?

Go to Step 13

--

12

Replace the BCM. Refer to Control Module References .

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