GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The body control module (BCM) controls the daytime running lamp (DRL) relay by grounding the control circuit of the DRL relay coil.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2602 Daytime Running Lamp Control Circuit Low

Conditions for Running the DTC

    • Voltage supplied to the module is in the normal operating voltage range, approximately 10-16 volts.
    • The DRL feature must be enabled.

Conditions for Setting the DTC

    • The BCM detects a short to ground or an open in the control circuit of the DRL relay coil when the daytime running lamps are inactive.
    • The condition must be present for more than 3 ms.

Action Taken When the DTC Sets

    • The BCM stores DTC B2602 in memory.
    • The BCM may store DTC B3857 in memory.
    • The SERVICE VEHICLE SOON telltale illuminates.

Conditions for Clearing the DTC

    • A current DTC B2602 clears if the BCM no longer detects a short to ground or an open in the control circuit of the DRL relay coil.
    • A current DTC B3857 clears if the BCM no longer detects a short to ground in the DRL relay control circuit.
    • A history DTC B2602 clears after 100 consecutive ignition cycles.
    • The BCM receives the Clear Code commend 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 .
    • An intermittent short to ground or an open in the following locations may cause an intermittent malfunction to occur:
       - The control circuit of the DRL relay coil
       - The DRL relay
       - The BCM

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 DRL relay ON and OFF.

Does the daytime running lamp (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. Probe the coil side supply circuit of the DRL relay with a test lamp that is connected to 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 DRL relay and the coil side supply circuit of the DRL relay.
  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 control circuit of the DRL relay for a poor connection 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 DRL 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 a poor connection at the DRL 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 a high resistance or a poor connection 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

Replace the underhood fuse block. Refer to Testing for Intermittent Conditions and Poor Connections .

Did you complete the repair?

Go to Step 13

--

11

Replace the DRL relay. Refer to Relay Replacement .

Did you complete the replacement?

Go to Step 13

--

12

Replace the BCM. Refer to Control Module References for 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