GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Camaro 🢒 Body and Accessories 🢒 Lighting Systems 🢒 DTC 021 and/or 031

Circuit Description

The body control module (BCM) supplies battery voltage to the courtesy lamps through the courtesy lamps supply voltage circuit when the BCM is awake. When the BCM sees the proper inputs it will ground the courtesy lamps low control circuit, and the courtesy lights will illuminate.

Conditions for Running the DTC

The BCM must command the courtesy lamps ON.

Conditions for Setting the DTC
    • The BCM detects that the output for the courtesy lamps supply voltage circuit is low when it is expected to be high.
    • There is an open or short to ground in the battery positive voltage circuit to the BCM that feeds 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 B21/31 in memory.

Conditions for Clearing the DTC
    • A current DTC B21/31 will clear if a short to ground or open in the courtesy lamps supply voltage circuit is no longer detected by the BCM.
    • A current DTC B21/31 will clear if the open or short to ground in the battery positive voltage circuit to the BCM that feeds the courtesy lamps supply voltage circuit is no longer present.
    • A history DTC B21/31 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 B21/31 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 ground or open in the courtesy lamps supply voltage circuit
       - An intermittent open or short to ground in the battery positive voltage circuit to the BCM that feeds the courtesy lamps supply voltage circuit
       - An intermittent short to ground in a courtesy lamp
       - The BCM is intermittently shorted to ground or open

Test Description

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

  1. Test for voltage at the courtesy lamps supply voltage circuit. No voltage at the courtesy lamps supply voltage circuit would indicate that the fault is current, voltage at the courtesy lamps supply voltage circuit would indicate that the fault is intermittent.

    2.

  2. Verifies that the COURTESY Fuse is good, an open fuse indicates a short to ground in the courtesy lamps supply voltage circuit or the battery positive voltage circuit of the BCM, that feeds the courtesy lamps supply voltage circuit.

  3. Verifies that the battery positive voltage circuit of the BCM is providing battery voltage.

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. Turn ON the ignition, with the engine OFF.
  2. Disconnect one of the courtesy lamps connectors.
  3. Probe the courtesy lamps supply voltage circuit of the courtesy lamp with a test lamp that is connected to ground.

Does the test lamp illuminate?

Go to Diagnostic Aids

Go to Step 3

3

Inspect the Courtesy Fuse for an open.

Is the courtesy fuse open?

Go to Step 8

Go to Step 4

4

  1. Disconnect the body control module (BCM) connectors.
  2. Probe the battery positive voltage circuit of the BCM that feeds the courtesy lamps supply voltage circuit with a test lamp that is connected to ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 9

5
  1. Connect a fused jumper between the battery positive voltage circuit and the courtesy lamps supply voltage circuit of the BCM connector. Refer to Circuit Testing in Wiring Systems.
  2. Probe the courtesy lamps supply voltage circuit of the courtesy lamp with a test lamp that is connected to ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 6

6

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

Did you complete the repair?

Go to Step 11

 

7

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 11

Go to Step 10

8

Repair the short to ground in the battery positive voltage circuit of the BCM that feeds the courtesy lamps supply voltage circuit or the courtesy lamps supply voltage circuit. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 11

--

9

Repair the open or high resistance in the battery positive voltage circuit of the BCM that feeds the courtesy lamps supply voltage circuit. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 11

--

10

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

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

Did you complete the replacement?

Go to Step 11

--

11
  1. Clear the DTC. Refer to On-Board Diagnostic Features in Body Control System.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
  3. Retrieve the DTCs. Refer to On-Board Diagnostic Features in Body Control System.

Does the DTC reset?

Go to Step 2

System OK