GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2002 🢒 Eldorado 🢒 DTC 🢒 DTC B2472

Circuit Description

The Body Control Module (BCM) supplies battery positive voltage to the HEADLAMP relay coil. The BCM provides ground to the HEADLAMP relay in the control circuit. The BCM monitors the voltage in the HEADLAMP relay control circuit every second.

Conditions for Running the DTC

A short to ground in the control circuit of the HEADLAMP relay will be tested when the following conditions are met:

    • The ignition is ON.
    • The HEADLAMP relay is de-energized.
    • The headlamp switch is in the OFF position.
    • DTC B1970 is not present.

A short to battery positive voltage in the control circuit of the HEADLAMP relay will be tested when the following conditions are met:

    • The ignition is ON.
    • The HEADLAMP relay is energized.
    • DTC B1970 is not present.

Conditions for Setting the DTC

One of the following conditions will cause this DTC to set:

    • The HEADLAMP relay is de-energized, and the BCM detects that the voltage in the control circuit of the HEADLAMP relay is low for at least 3 seconds.
    • The HEADLAMP relay is energized, and the BCM detects that the control circuit of the HEADLAMP relay is high for at least 3 seconds.

Action Taken When the DTC Sets

The BCM turns OFF the HEADLAMP relay output, until the condition for setting the DTC is no longer present.

Conditions for Clearing the DTC

The DTC will clear when the following conditions are met:

    • The BCM detects that the voltage in the control circuit of the HEADLAMP relay is no longer low for at least 3 seconds.
    • The BCM detects that the control circuit of the HEADLAMP relay is no longer high for at least 3 seconds.

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.

  2. Tests for voltage at the coil side of the HEADLAMP relay . The BCM supplies power to the coil side of the HEADLAMP relay through the headlamp relay coil supply voltage circuit.

    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 Lighting Systems 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 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. Connect a test lamp between the supply voltage circuit of the HEADLAMP relay coil and a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 11

4

  1. Connect a test lamp between the control circuit of the HEADLAMP relay and the supply voltage circuit of the HEADLAMP relay coil.
  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 5

5

Does the test lamp remain illuminated with each command?

Go to Step 6

Go to Step 7

6
  1. Disconnect the headlamp switch.
  2. With a scan tool, command the HEADLAMP relay ON and OFF.

Does the test lamp remain illuminated with each command?

Go to Step 8

Go to Step 13

7

Test the control circuit of the HEADLAMP relay for a short to voltage or an open. 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 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 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 12

10

Inspect for poor connections at the harness connector of the Body Control Module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

11

Repair an open or high resistance in the supply voltage circuit of the HEADLAMP relay coil. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 15

--

12

Replace the HEADLAMP relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 15

--

13

Replace the headlamp switch. Refer to Headlamp Switch Replacement

Did you complete the replacement?

Go to Step 15

--

14

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