GM Service Manual Online
For 1990-2009 cars only

Circuit Description

Ground is applied to the turn signal switch. When the turn signal switch is placed in the turn left position, ground is applied to the BCM through the left turn signal switch circuit. The BCM then applies a pulsating voltage to the LF and LR turn signal lamps through the LF and LR turn signal voltage supply circuits.

Conditions for Running the DTC

The battery voltage must be between 9.0-14 volts.

Conditions for Setting the DTC

    • DTC B3950 02 A short to ground in the LR turn signal voltage supply circuit is present for longer than 0.1 seconds.
    • DTC B3950 05 A short to battery positive voltage or an open is detected in the LR turn signal voltage supply circuit is present for longer than 1 second.

Action Taken When the DTC Sets

    • If DTC B3950 02 sets, the left rear turn signal lamp does not work.
    • If DTC B3950 05 sets, if the LR turn signal voltage supply circuit is shorted to battery positive voltage the left rear turn signal lamp will be on at all times and if the LR turn signal voltage supply circuit is open the left rear turn signal lamp will be inoperative.

Conditions for Clearing the DTC

    • The DTC will clear on current status after the condition for setting the fault is corrected.
    • DTC B3950 02 will set a history code which will clear after 100 consecutive ignition cycles without a fault present.
    • History and current DTCs can be cleared using a scan tool.

Diagnostic Aids

    • Check the LR turn lamp LEDs. If the LEDs are open, DTC B3950 05 will be set.
    • If the DTC is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • An intermittent short to ground or an open in the following locations may cause an intermittent malfunction to occur:
       - The BCM
       - The left rear turn signal supply voltage circuit

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?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Turn ON the ignition, with the engine OFF.
  2. Place the turn signal switch in the TURN LEFT position.

Do the rear turn signal lamps flash ON and OFF?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Is DTC B3950 02 set?

Go to Step 4

Go to Step 5

4

  1. Turn OFF the ignition.
  2. Disconnect the BCM harness connector C3.
  3. Disconnect the LH tail lamp assembly.
  4. Connect a test lamp between battery positive voltage and the LR turn signal voltage supply circuit at the BCM harness connector C3.

Does the test lamp illuminate?

Go to Step 10

Go to Step 8

5

Is the LR turn signal lamp on at all times?

Go to Step 6

Go to Step 7

6

Disconnect the BCM harness connector C3.

Does the LR turn lamp turn OFF?

Go to Step 8

Go to Step 9

7

  1. Disconnect the BCM harness connector C3.
  2. Test for continuity in the LR turn signal voltage supply circuit between the BCM harness connector C3 and the LH tail lamp assembly. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 8

8

Inspect for a high resistance or an open at the harness connector of the BCM. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 11

9

Repair a short to battery positive voltage in the LR turn signal lamp voltage supply circuit. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 12

--

10

Repair a short to ground in the LR turn signal voltage supply circuit. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 12

--

11

Important: After replacing the BCM, perform the setup procedure. Refer to Body Control Module (BCM) Programming/RPO Configuration in Computer/Integrating Systems.

Replace the BCM. Refer to Body Control Module Replacement in Computer/Integration Systems.

Did you complete the replacement?

Go to Step 12

--

12

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

Go to Step 2

System OK