GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The body control module (BCM) controls the DRL relay. The BCM grounds the DRL relay coil control circuit, which energizes the DRL relay.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2602 DRL Control Circuit Low

Conditions for Running the DTC

The BCM must not be commanding the DRL relay to energize.

Conditions for Setting the DTC

    • The BCM detects a short to ground or open in the DRL relay coil control circuit.
    • The condition above must be present for more than 0.3 seconds.

Action Taken When the DTC Sets

The BCM stores DTC B2602 in memory.

Conditions for Clearing the DTC

    • A current DTC B2602 will clear if the BCM no longer detects a short to ground or open in the DRL relay coil control circuit.
    • A history DTC B2602 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

Diagnostic Aids

    • If the DTC B2602 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • The following conditions may cause an intermittent malfunction to occur:
       - An intermittent short to ground or open in the DRL relay coil control circuit
       - The DRL relay coil is intermittently shorted to ground or open internally.
       - The BCM is intermittently shorted to ground or open internally.

Step

Action

Yes

No

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

Connector End View Reference: Master Electrical Component List in Wiring Systems

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 DRL relay ON and OFF.

Does the DRL relay turn ON and OFF with each command?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the DRL relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Using a test lamp connected to ground, probe the DRL relay coil side voltage supply circuit.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between the DRL relay coil side voltage supply and the DRL relay control circuit.
  2. With a scan tool, command the DRL 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 DRL relay control circuit for a short to battery positive voltage or an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 9

7

Test the DRL relay control circuit for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 9

8

Inspect for poor connections at the DRL 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 14

Go to Step 12

9

Inspect for poor connections at the harness connector of the body control module. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 13

10

Test for a high resistance or the open in the DRL relay coil side voltage supply circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 11

11

Replace the underhood junction block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.

Did you complete the repair?

Go to Step 14

--

12

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

Did you complete the replacement?

Go to Step 14

--

13

Replace the body control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup and programming.

Did you complete the replacement?

Go to Step 14

--

14

  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