GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The body control module (BCM) controls the instrument panel (I/P) courtesy lamps through the courtesy lamps supply voltage circuit. The BCM grounds the courtesy lamps low control circuit which completes the I/P courtesy lamps ground circuit, and the lights illuminate.

Conditions for Running the DTC

The BCM must command the courtesy lamps feature ON.

Conditions for Setting the DTC

    • The BCM detects a high when the output should be low in the courtesy lamps supply voltage circuit.
    • The condition above must be present for more than 0.3 seconds.

Action Taken When the DTC Sets

The BCM stores DTC B2618 in memory.

Conditions for Clearing the DTC

    • A current DTC B2618 will clear if the short to battery in the courtesy lamps supply voltage circuit is no longer detected by the BCM.
    • A history DTC B2618 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present and no other BCM faults are detected.

Diagnostic Aids

    • If the DTC B2618 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 courtesy lamps supply voltage circuit.
       - Either I/P courtesy lamp is intermittently shorted to battery internally.
       - The BCM is intermittently shorted to battery internally.

Step

Action

Yes

No

Schematic Reference: Interior Lights 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 light test - theater dimming #1 output to ON and OFF.

Do the footwell lamps turn ON and OFF with each command?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the instrument panel (I/P) courtesy lamps.
  3. Turn ON the ignition, with the engine OFF.
  4. Using a test lamp connected to ground, probe the courtesy lamps supply voltage circuit.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between the courtesy lamps supply voltage and the courtesy lamps low control circuit.
  2. With a scan tool, command the light test - theater dimming #1 output 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 courtesy lamps low control circuit for high resistance or an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the courtesy lamps low 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 13

Go to Step 9

8

Inspect for poor connections at each I/P courtesy lamp. 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 13

Go to Step 11

9

Inspect for poor connections at the harness connector of the BCM. 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 13

Go to Step 12

10

Repair the high resistance or an open in the courtesy lamps supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

Replace the inoperative I/P courtesy lamp. Refer to Instrument Panel Courtesy Lamp Bulb Replacement

Did you complete the replacement?

Go to Step 13

--

12

Important: Perform the set up procedure for the BCM. Refer to Body Control Module (BCM) Programming/RPO Configuration in Body Control System.

Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 13

--

13

  1. Use the scan tool in order to clear the DTC.
  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