Diagnostic Aids

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.

An open or short to ground in the battery positive voltage circuit of the STOP/TURN fuse will cause all 4 turn signal DTCs.
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 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 underhood electrical center
- The left front turn signal lamp 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 Diagnostic System Check - Vehicle?	Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Turn ON the ignition, with the engine OFF. Place the turn signal switch in the left turn position. Does the LF turn signal lamp flash ON and OFF?	Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems	Go to Step 3
3	Remove the LF turn signal bulb. Refer to Daytime Running Lamp, Park and Turn Signal Lamp and Bulb Replacement - Front . Inspect the bulb filament. Is the bulb OK?	Go to Step 4	Go to Step 8
4	Test the ground circuit of the inoperative lamp for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 10	Go to Step 5
5	Test the left front turn signal supply voltage circuit for the following: A short to ground A high resistance An open Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 10	Go to Step 7
6	Test the battery positive voltage circuit from the STOP/TURN fuse for a short to ground or an open. Did you find and correct the condition?	Go to Step 10	Go to Step 7
7	Inspect for a high resistance or an open at the harness connector of the body control module (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 10	Go to Step 9
8	Replace the bulb. Refer to Daytime Running Lamp, Park and Turn Signal Lamp and Bulb Replacement - Front . Did you complete the replacement?	Go to Step 10	-
9	Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup and programming. Did you complete the replacement?	Go to Step 10	-
10	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 3	System OK