AutoCodes – GMC – B3950 GMC

B3950 GMC 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 GMC 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 1,720

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

What does this mean?

What are the Possible Causes of the DTC B3950 GMC?

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 GMC?

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 GMC 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.

Need more information about the B3950 GMC code?

Need more information on how to fix the B3950 GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

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Information for Specific GMC Models

B3950 2014 GMC Sierra — Left Rear Turn Signal Circuit
B3950 2015 GMC Sierra — Left Rear Turn Signal Circuit
B3950 2016 GMC Sierra — Left Rear Turn Signal Circuit
B3950 2017 GMC Sierra — Left Rear Turn Signal Circuit
B3950 2018 GMC Sierra — 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 GMC Code

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

When this code is triggered, you may notice that the left rear turn signal on your GMC vehicle does not illuminate or blink as intended.

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

Some common causes of this code include a faulty left rear turn signal bulb, a damaged wiring harness in the left rear turn signal circuit, or a defective turn signal flasher relay.

3. How can I diagnose the issue causing OBDII code B3950 GMC?

To diagnose the problem, start by inspecting the left rear turn signal bulb for any signs of damage. Then, check the wiring harness for any visible issues such as frayed wires or loose connections.

4. Can a blown fuse cause OBDII code B3950 GMC to be triggered?

While a blown fuse in the left rear turn signal circuit can potentially cause this code, it is more likely to result in a loss of power to the turn signal rather than triggering the specific B3950 code.

5. Is it safe to continue driving with OBDII code B3950 GMC active?

It is not recommended to drive with this code active, as it indicates a malfunction in the left rear turn signal circuit, which can pose a safety hazard by affecting the visibility of your turning intentions to other drivers.

6. How can I repair OBDII code B3950 GMC on my GMC vehicle?

To repair this code, you may need to replace the left rear turn signal bulb, repair any damaged wiring in the circuit, or replace the turn signal flasher relay if it is found to be faulty.

7. Will resetting the OBDII code B3950 GMC clear the issue permanently?

Resetting the code may temporarily clear the issue, but if the underlying problem causing the code to be triggered is not addressed, it is likely to reappear upon the next diagnostic scan.

8. Are there any specific GMC models known to be more prone to experiencing OBDII code B3950?

While this code can potentially occur in various GMC models, certain older vehicles or those with high mileage may be more susceptible to issues in the turn signal circuits.

9. Can extreme weather conditions impact the likelihood of OBDII code B3950 GMC being triggered?

Extreme weather conditions, such as heavy rain or snow, can sometimes contribute to electrical issues in the turn signal circuit, which may increase the chances of triggering this specific OBDII code.

10. How can regular maintenance help prevent OBDII code B3950 GMC from occurring?

Regularly inspecting and maintaining your vehicle's turn signal components, including bulbs and wiring, can help prevent issues that could lead to the triggering of OBDII code B3950 GMC.