GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 SSR 🢒 Restraints 🢒 SIR 🢒 DTC B2600

Circuit Description

The ambient light sensor is a light sensitive transistor that sends a variable voltage signal to the body control module (BCM) in response to the exterior light level. The BCM energizes the daytime running lamp (DRL) relays by grounding the DRL relay control circuits. The DRL operate when the ambient light sensor indicates daytime, the ignition switch is in the RUN position, the gear selector is not in the park or neutral position, and the parking brake is released.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2600 Daytime Running Lamp Control Circuit

Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

Conditions for Setting the DTC
    • When the BCM sends a DRL OFF command and one of the DRL relay control circuits are shorted to ground
    • When the BCM sends a DRL ON command and one of the DRL relay control circuits are shorted to voltage or open
    • When the DRL diode supply voltage circuit is shorted to ground
    • When the battery positive supply voltage circuit is shorted to ground or open

Action Taken When the DTC Sets

The DRL will not operate or will remain always ON.

Conditions for Clearing the MIL/DTC
    • This DTC will clear on current status after the condition for setting the fault is corrected.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • History and current DTCs can be cleared using a scan tool.

Test Description

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

  1. Listen for an audible click when the DRL relays operate. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. This step tests for voltage at the coil side of the DRL relays.

    3.

  3. This step verifies that the BCM is providing ground to the DRL relays.

    4.

  4. This step tests if ground is constantly being applied to the DRL relays.

    5.

  5. This step tests if there is opposing voltage present or an open in the DRL relay control circuits.

    6.

  6. After replacement of the BCM you must calibrate the new module for proper operation.

Step

Action

Yes

No

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

Connector End View Reference: Lighting Systems Connector End Views or Computer/Integrating Systems Connector End Views in Computer/Integrating 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 relays ON and OFF.

Do the DRL relays 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 daytime running lamp (DRL) relays.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the battery positive voltage circuit of each of the DRL relays and 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 and the battery positive voltage circuit of each of the DRL relays.
  2. With a scan tool, command the DRL relays 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 circuits of the DRL relays for high resistance, an open, a short to voltage or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the control circuits of the DRL relays 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 13

Go to Step 9

8

Inspect for poor connections at the inoperable DRL relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

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 Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair the short to ground, open, or high resistance in one of the following circuits. Refer to Wiring Repairs in Wiring Systems.

    • Battery positive supply voltage
    • DRL diode supply voltage
    • Right headlamp low beam supply
    • Left headlamp low beam supply

Did you complete the repair?

Go to Step 13

--

11

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

Did you complete the replacement?

Go to Step 13

--

12

Replace the BCM. Refer to Control Module References in Computer/Integrating Systems 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