GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The body control module (BCM) turns on the LOW BEAM relay when the ambient light sensor senses a dark condition or the low beam headlamps are requested ON. Battery positive voltage is supplied to the LOW BEAM relay at all times. The BCM grounds the LOW BEAM relay control circuit in order to activate the relay.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2575 Headlamp Control Circuit

Conditions for Running the DTC

    • The ignition switch is in the ON position.
    • The ambient light sensor senses a dark condition, automatic lamp control (ALC) headlamps ON.

Conditions for Setting the DTC

    • B2575 01 will set if there is a short to voltage in the low beam relay control circuit.
    • B2575 06 will set if there is an open or short to ground in the low beam relay control circuit.

Action Taken When the DTC Sets

    • The SERVICE indicator illuminates.
    • 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

    • Turn the ignition switch to the OFF position, cover the ambient light sensor on the dash, wait for 15 seconds, and then return the ignition to the ON position. The low beam headlamps should illuminate.
    • If the DTC is a history DTC, the problem may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .

Test Description

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

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

  2. This step tests for voltage at the coil side of the LOW BEAM relay.

Step

Action

Yes

No

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

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the LOW BEAM relay ON and OFF.

Does the LOW BEAM relay turn ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

Is DTC B2575.01 set?

Go to Step 6

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the LOW BEAM relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the coil side battery positive voltage circuit of the LOW BEAM relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 10

5

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

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

Go to Step 8

Go to Step 7

6

Test the control circuit of the LOW BEAM relay for a short to voltage. 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 LOW BEAM relay for a high resistance 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

8

Inspect for poor connections at the LOW BEAM relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector 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 Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair the open in the coil side battery positive voltage circuit of the LOW BEAM relay. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 13

--

11

Replace the 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 for BCM 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