AutoCodes – Generic – B3948

B3948 Code - Left Front Turn Signal Circuit

Quick Answer

Ground is applied at all times to the turn signal/multifunction switch. Common causes include Faulty Left Front Turn Signal Lamp, Left Front Turn Signal Lamp harness is open or shorted, Left Front Turn Signal Lamp circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: B3948 indicates Left Front Turn Signal Circuit.
Common causes: Common causes include Faulty Left Front Turn Signal Lamp, Left Front Turn Signal Lamp harness is open or shorted, Left Front Turn Signal Lamp circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 5,544

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 17, 2023

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code B3948 Description

Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START positions. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the Body Control Module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM responds to the turn signal switch input by applying a pulsating voltage to the front and rear turn signal lamps through there respective control circuits. When a turn signal request is received by the BCM, a serial data message is sent to the instrument cluster requesting the respective turn signal indicator be pulsed ON and OFF. The Diagnostic Trouble Code (DTC) will be set when the BCM detects an open/high resistance in the left front turn signal control circuit.

OBDII Code B3948 - Left Front Turn Signal Circuit - AutoCodes.com — B3948 Code - Left Front Turn Signal Circuit

What does this mean?

What are the Possible Causes of the DTC B3948?

Faulty Left Front Turn Signal Lamp
Left Front Turn Signal Lamp harness is open or shorted
Left Front Turn Signal Lamp circuit poor electrical connection
Faulty Body Control Module (BCM)

How to Fix the DTC B3948?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B3948 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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Need Help with the Code?

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Information for Specific Makes

B3948 Buick — Left Front Turn Signal Circuit
B3948 Cadillac — Left Front Turn Signal Circuit
B3948 Chevrolet — Left Front Turn Signal Circuit
B3948 GMC — Left Front Turn Signal Circuit
B3948 Pontiac — Left Front Turn Signal Circuit
B3948 Saturn — Left Front Turn Signal Circuit

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about B3948 Code

1. What are common symptoms of OBDII code B3948 (Left Front Turn Signal Circuit)?

The common symptoms include the left front turn signal not working, rapid blinking of the turn signal, or a warning light on the dashboard indicating a problem with the turn signal.

2. What are the possible causes of OBDII code B3948?

Possible causes of this code include a faulty turn signal bulb, a damaged wiring harness, a malfunctioning turn signal switch, or a problem with the turn signal relay.

3. How can I diagnose the issue related to OBDII code B3948?

You can start by visually inspecting the left front turn signal bulb, checking the wiring for any visible damage, and testing the turn signal switch and relay using a multimeter.

4. Can a blown fuse cause OBDII code B3948 to appear?

Yes, a blown fuse in the turn signal circuit can trigger this OBDII code. Check and replace any blown fuses as part of your troubleshooting process.

5. What are some repair tips for fixing OBDII code B3948?

Repair tips include replacing the left front turn signal bulb if it's faulty, repairing or replacing damaged wiring, and ensuring the turn signal switch and relay are functioning properly.

6. Is it safe to continue driving with OBDII code B3948 triggered?

It is not recommended to drive with a malfunctioning turn signal as it can pose a safety hazard on the road. Promptly address and repair the issue to ensure proper signaling while driving.

7. Can moisture or water damage cause OBDII code B3948?

Yes, moisture or water ingress into the turn signal assembly or wiring can lead to electrical issues that trigger this OBDII code. Check for any signs of water damage during your inspection.

8. Do I need specialized tools to fix OBDII code B3948?

While basic tools like a multimeter and screwdrivers are typically sufficient for diagnosing and repairing this code, specialized tools may be needed depending on the exact cause of the turn signal circuit issue.

9. How much does it cost to repair OBDII code B3948 at a mechanic or dealership?

The cost of repairing this OBDII code can vary depending on the underlying issue, but it may range from $50 to $200 for parts and labor at a mechanic or dealership.

10. Will resetting the OBDII system clear code B3948?

Resetting the OBDII system may temporarily clear the code, but if the underlying issue causing OBDII code B3948 is not addressed, the code is likely to reappear. It's important to diagnose and fix the root cause of the problem.