AutoCodes – Generic – B3950

B3950 Code - Left Rear Turn Signal Circuit

Quick Answer

Ground is applied at all times to the turn signal/multifunction switch. Common causes include Faulty Left Rear Turn Signal Lamp, Left Rear Turn Signal Lamp harness is open or shorted, Left Rear 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: B3950 indicates Left Rear Turn Signal Circuit.
Common causes: Common causes include Faulty Left Rear Turn Signal Lamp, Left Rear Turn Signal Lamp harness is open or shorted, Left Rear 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 4,277

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Basic DIY (1 / 3)

What is this?

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

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code B3950 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 a short to voltage, short to ground, or an open/high resistance in the left rear turn signal control circuit.

OBDII Code B3950 - Left Rear Turn Signal Circuit - AutoCodes.com — B3950 Code - Left Rear Turn Signal Circuit

What does this mean?

What are the Possible Causes of the DTC B3950?

Faulty Left Rear Turn Signal Lamp
Left Rear Turn Signal Lamp harness is open or shorted
Left Rear Turn Signal Lamp circuit poor electrical connection

How to Fix the DTC B3950?

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 does this mean?

Code Tech Notes

B3950:01 Left Rear Turn Signal Circuit Short to Battery
B3950:02 Left Rear Turn Signal Circuit Short to Ground
B3950:04 Left Rear Turn Signal Circuit Open

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B3950 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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Information for Specific Makes

B3950 Buick — Left Rear Turn Signal Circuit
B3950 Cadillac — Left Rear Turn Signal Circuit
B3950 Chevrolet — Left Rear Turn Signal Circuit
B3950 GMC — Left Rear Turn Signal Circuit
B3950 Pontiac — Left Rear Turn Signal Circuit
B3950 Saturn — Left Rear 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 B3950 Code

1. What are the common symptoms of OBDII code B3950 - Left Rear Turn Signal Circuit?

- Common symptoms include a non-functioning left rear turn signal, fast blinking turn signal indicator, or a warning light on the dashboard.

2. What are the possible causes of OBDII code B3950?

- Possible causes include a faulty left rear turn signal bulb, a damaged wiring harness, a defective turn signal switch, or a malfunctioning body control module.

3. How can I diagnose the issue related to OBDII code B3950?

- You can start by visually inspecting the left rear turn signal bulb and the wiring for any damage. Use a multimeter to test the continuity of the wiring and check for proper voltage at the bulb socket.

4. Can a loose or corroded connection cause OBDII code B3950?

- Yes, a loose or corroded connection in the left rear turn signal circuit can trigger code B3950. Make sure all connections are secure and free of corrosion.

5. What is the recommended repair for OBDII code B3950?

- The recommended repair involves addressing the specific issue causing the left rear turn signal circuit malfunction. This may include replacing a faulty bulb, repairing damaged wiring, or replacing a defective component like the turn signal switch.

6. Can I clear OBDII code B3950 without fixing the underlying issue?

- Clearing the code without fixing the underlying issue may temporarily turn off the warning light, but the problem will persist, and the code is likely to return. It is best to address the root cause of the issue.

7. Is it safe to drive with OBDII code B3950 active?

- It is generally safe to drive with code B3950, but you may face issues with turn signal functionality, affecting your vehicle's safety and compliance with road regulations. It is recommended to address the issue promptly.

8. How do I reset OBDII code B3950 after making repairs?

- After making necessary repairs to the left rear turn signal circuit, you can reset the code by using an OBDII scanner or disconnecting the vehicle's battery for a few minutes. Be sure to follow proper procedures to avoid any complications.

9. Can extreme weather conditions affect OBDII code B3950?

- Extreme weather conditions, especially moisture and corrosion, can exacerbate issues with the left rear turn signal circuit, potentially triggering code B3950. Proper maintenance and protection against the elements can help prevent such problems.

10. Should I seek professional help for diagnosing and repairing OBDII code B3950?

- If you are not familiar with automotive electrical systems or troubleshooting procedures, it is recommended to seek professional help to accurately diagnose and repair OBDII code B3950. A certified mechanic or auto electrician can help resolve the issue efficiently.