Diagnostic Aids

WARNING: This page is about a different car, the 2004 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.

Check the LF turn lamp bulb. If the bulb is open, DTC B3948 will be set.
If the DTC is a history DTC, the fault may be interment. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
An interment short to ground or an open in the following locations may cause an intermittent malfunction to occur:
- The BCM
- The underhood electrical center
- The left front turn signal supply voltage circuit

DTC B3948

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 Lighting System Diagnostic System Check?	Go to Step 2	Go to Diagnostic System Check - Lighting Systems
2	Turn ON the ignition, with the engine OFF. Place the turn signal switch in the TURN LEFT position. Do the front left turn signal lamps flash on and off?	Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems	Go to Step 3
3	Turn OFF the ignition. Disconnect the BCM harness connector C1. Remove the LF turn lamp bulb. Connect a test lamp between battery positive voltage and the LF turn signal voltage supply circuit at the BCM harness connector C1. Does the test lamp illuminate?	Go to Step 4	Go to Step 5
4	Test the LF turn signal voltage supply 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 12	Go to Step 8
5	Test for continuity in the LF turn signal voltage supply circuit between the BCM harness connector C1 and the LF turn signal lamp. Refer to Circuit Testing in Wiring Systems. Is the continuity in the circuit?	Go to Step 9	Go to Step 6
6	Disconnect the underhood electrical center. Test for continuity in the LF turn signal voltage supply circuit between the BCM harness connector C1 and the underhood fuse block. 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 7
7	Test for continuity in the LF turn signal voltage supply circuit between the underhood electrical center and the LF turn signal lamp. 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 underhood electrical center. 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 12	Go to Step 10
9	Inspect for a high resistance or an open at the harness connector of the 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 12	Go to Step 11
10	Replace the underhood electrical center. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems. Did you complete the replacement?	Go to Step 12	-
11	IMPORTANT: After replacing the BCM, perform the setup procedure. 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 12	-
12	Use the scan tool in order to clear the DTCs. Operate the vehicle within the Conditions for Running the DTC. Does the DTC reset?	Go to Step 2	System OK