GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2001 🢒 Regal (China) 🢒 DTC 🢒 DTC B2602

Circuit Description

The BCM communicates with the automatic headlamp control module through the automatic headlamp link circuit in order to determine day or night operation. The BCM communicates this information to the instrument cluster through the Class 2 serial data link.

Conditions for Setting the DTC

The BCM detects a short to ground or an open in the automatic headlamp link circuit when turning the ignition switch from CRANK to ON.

Action Taken When the DTC Sets

The BCM will operate in day mode.

Conditions for Clearing the DTC
    • When the ignition switch is turned from OFF to ON, a current DTC B2602 is always cleared. If a short to ground or open is still present when the ignition switch is turned from START to ON, DTC B2602 will reset as a current DTC.
    • A history DTC will clear after 100 consecutive ignition cycles if the condition for the fault is no longer present.
    • The BCM receives a clear code command from the scan tool.

Diagnostic Aids
    • If the DTC B2602 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .
    • The following conditions may cause an intermittent malfunction to occur:
       - An intermittent short to ground in the automatic headlamp link circuit.
       - An intermittent open in the automatic headlamp link circuit
       - The automatic headlamp module is shorted to ground or open internally.

Test Description

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

  1. Check for an open in the automatic headlamp link circuit.

    2.

  2. This step checks for a short to ground in the automatic headlamp circuit.

    3.

  3. This step test for voltage on the automatic headlamp link circuit.

    4.

  4. This step checks for a voltage to the automatic headlamp control module.

Step

Action

Yes

No

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

1

Did you perform the Lighting System Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

Test the automatic headlamp link circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 3

3

Test the automatic headlamp link circuit 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 9

Go to Step 4

4

  1. Connect the automatic headlamps control module connector.
  2. Disconnect the Body Control Module (BCM) connector C1.
  3. Turn the ignition switch to the ON position.
  4. Probe the automatic headlamp link circuit of the BCM harness connector with a test lamp that is connected to ground.

Does the test light illuminate?

Go to Step 5

Go to Step 6

5
  1. Disconnect the automatic headlamps control module connector.
  2. Connect the Body Control Module (BCM) connector C1.
  3. Turn the ignition switch to the ON position.
  4. Probe the automatic headlamp link circuit of the automatic headlamp control module harness connector with a test lamp that is connected to battery voltage.

Does the test light illuminate?

Go to Step 8

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

6

Test the battery positive voltage circuit of the automatic headlamp control module for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 7

7

Replace the automatic headlamp control module. Refer to Headlamp Control Module Replacement .

Is the repair complete?

Go to Step 9

--

8

Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Is the repair complete?

Go to Step 9

--

9
  1. Turn the ignition switch to the OFF position.
  2. Connect the connectors and reinstall the components that were removed.
  3. Turn the ignition switch to the ON position.
  4. Clear the DTCs.
  5. Test for DTCs.

Are any current DTCs set?

Go to Diagnostic System Check - Lighting Systems

System OK