GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Century 🢒 DTC 🢒 DTC B2603

Circuit Description

The body control module (BCM) illuminates LF turn signal lamp during Daytime Running Lamps (DRL) operation in the day mode. The BCM applies steady power to the LF turn signal lamp which illuminates the LF turn lamp in a non flashing mode.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2603 DRL Control Left Circuit High

Conditions for Running the DTC

The BCM must be commanding the LF turn signal lamp on.

Conditions for Setting the DTC
    • The BCM detects a short to battery positive voltage in the LF turn signal lamp supply voltage circuit or the LF turn signal switch signal circuit.
    • The condition above must be present for more than 20 seconds.

Action Taken When the DTC Sets

The BCM stores DTC B2603 in memory.

Conditions for Clearing the DTC
    • A current DTC B2603 will clear if the BCM no longer detects a short to battery positive voltage in LF turn signal lamp supply voltage circuit or the LF turn signal switch signal circuit.
    • A history DTC B2603 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • The BCM receives a clear code command from the scan tool.

Diagnostic Aids
    • If the DTC B2603 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 battery in the LF turn signal lamp supply voltage circuit or the LF turn signal switch signal circuit
       - The BCM is intermittently shorted to battery.

Step

Action

Yes

No

Schematic Reference: Exterior Lights 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 LF turn signal lamp control ON and OFF.

Does the LF turn signal lamp turn ON and OFF with each command?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the LF turn signal lamp.
  3. Turn ON the ignition, with the engine OFF.
  4. Using a test lamp connected to ground, probe the LF turn signal lamp supply voltage circuit.

Does the test lamp illuminate?

Go to Step 4

Go to Step 6

4

Test the LF turn signal supply battery positive voltage circuit 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 7

Go to Step 5

5

Test the LF turn signal switch signal circuit of the turn signal switch for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6

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

Did you complete the replacement?

Go to Step 7

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7
  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