AutoCodes – Generic – B3950:04

B3950:04 Code - Left Rear Turn Signal Circuit Open

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: B3950:04 indicates Left Rear Turn Signal Circuit Open.
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 431

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 B3950:04 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 rear turn signal control circuit.

OBDII Code B3950:04 - Left Rear Turn Signal Circuit Open - AutoCodes.com — B3950:04 Code - Left Rear Turn Signal Circuit Open

What does this mean?

What are the Possible Causes of the DTC B3950:04?

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 B3950:04?

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 B3950:04 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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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 B3950:04 Code

1. What are the common symptoms of OBDII code B3950:04 (Left Rear Turn Signal Circuit Open)?

The common symptoms include the left rear turn signal not functioning, fast blinking of the turn signal indicator on the dashboard, or a warning message on the vehicle's display.

2. What are the possible causes of the OBDII code B3950:04 (Left Rear Turn Signal Circuit Open)?

Possible causes include a faulty turn signal bulb, a broken or damaged wiring harness, a loose connection in the turn signal circuit, or a malfunctioning turn signal relay.

3. How can I diagnose the OBDII code B3950:04 (Left Rear Turn Signal Circuit Open)?

To diagnose the issue, you can visually inspect the left rear turn signal bulb and wiring for any visible damage. Using a multimeter, you can test the continuity of the wiring and connections in the circuit to identify any open circuits.

4. Is it safe to continue driving with the OBDII code B3950:04 (Left Rear Turn Signal Circuit Open)?

It is not recommended to drive with a malfunctioning turn signal, as it can pose a safety hazard to you and other drivers on the road. It's best to address the issue promptly.

5. How can I repair the OBDII code B3950:04 (Left Rear Turn Signal Circuit Open)?

Repairing the issue may involve replacing the faulty turn signal bulb, repairing or replacing the damaged wiring harness, securing any loose connections, or replacing the turn signal relay if necessary.

6. Can a DIY enthusiast fix the OBDII code B3950:04 (Left Rear Turn Signal Circuit Open)?

Depending on your skill level and experience with automotive repairs, you may be able to address this issue yourself. However, if you are unsure or uncomfortable working on electrical components, it's best to seek professional help.

7. Will resetting the OBDII code B3950:04 (Left Rear Turn Signal Circuit Open) make the problem go away?

Simply resetting the code will not fix the underlying issue causing the left rear turn signal circuit to be open. It's important to diagnose and repair the root cause of the problem to prevent the code from reappearing.

8. How much does it typically cost to repair the OBDII code B3950:04 (Left Rear Turn Signal Circuit Open)?

The cost of repair can vary depending on the specific cause of the issue, the extent of the damage, and whether you choose to repair it yourself or take it to a professional mechanic. Costs may range from replacing a bulb for a few dollars to replacing a wiring harness for a few hundred dollars.

9. Are there any preventive measures to avoid OBDII code B3950:04 (Left Rear Turn Signal Circuit Open) in the future?

Regularly checking and maintaining your vehicle's lighting system, including the turn signals, can help prevent issues like an open circuit in the left rear turn signal. Addressing any electrical problems promptly can also help prevent this code from appearing.