GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2001 🢒 Alero 🢒 DTC 🢒 DTC B2603

Circuit Description

The daytime running lamps (DRL) relay is controlled by the body control module (BCM). Ignition positive voltage is applied to the DRL relay coil. The BCM grounds the DRL relay control circuit in order to turn on the DRL relay. When the DRL relay control circuit becomes shorted to battery positive voltage, DTC B2603 is set.

Conditions for Running the DTC

The ignition switch is in the ON position.

Conditions for Setting the DTC
    • The BCM is commanding the DRL relay on.
    • The headlamp feedback is not present for 1 second.

Action Taken When the DTC Sets
    • The BCM disables the DRL relay control as long as the malfunction is present.
    • The SERVICE indicator illuminates.

Conditions for Clearing the DTC
    • The conditions for setting the DTC are no longer present.
    • A history DTC clears after 100 malfunction free ignition cycles.
    • The BCM receives the clear code command from the scan tool.

Diagnostic Aids
    • The park brake must be unapplied and the transaxle must be in gear for the DRLs to operate properly.
    • If the DTC is a history DTC, the problem may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the daytime running lights (DRL) relay ON and OFF.

Does the DRL 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 DRL relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the control 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 5

4

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

Did you find and correct the condition?

Go to Step 9

Go to Step 6

5

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 9

Go to Step 7

6

Inspect for poor connections at the harness connector of the body control module (BCM). 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 9

Go to Step 8

7

Replace the DRL relay.

Did you complete the repair?

Go to Step 9

--

8

Important: Perform the set up procedure for the body control module.

Replace the body control module. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 9

--

9
  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