AutoCodes – GMC – B3948 2017 GMC Sierra

B3948 2017 GMC Sierra 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 2017 GMC Sierra 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 157
How popular is this code, among other codes? Low
Table of contents Created and updated by William Orellana on Jun 17, 2023
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Code B3948 2017 GMC Sierra 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 2017 GMC Sierra - Left Front Turn Signal Circuit - AutoCodes.com
B3948 2017 GMC Sierra Code - Left Front Turn Signal Circuit

What are the Possible Causes of the DTC B3948 2017 GMC Sierra?

  • 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 2017 GMC Sierra?

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 2017 GMC Sierra 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 B3948 2017 GMC Sierra code?

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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 B3948 2017 GMC Sierra Code

1. What are the common symptoms of OBDII code B3948 in a 2017 GMC Sierra related to the left front turn signal circuit?

The common symptoms include the left front turn signal not functioning properly, such as flickering, staying on constantly, or not illuminating at all.

2. What are some possible causes of OBDII code B3948 in a 2017 GMC Sierra regarding the left front turn signal circuit?

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

3. How can I diagnose the underlying issue causing OBDII code B3948 in my 2017 GMC Sierra's left front turn signal circuit?

You can start by visually inspecting the left front turn signal bulb, checking the wiring for any damage, testing the turn signal switch, and using a scan tool to gather more diagnostic information.

4. Are there any quick repair tips for fixing OBDII code B3948 in a 2017 GMC Sierra related to the left front turn signal circuit?

You can try replacing the left front turn signal bulb first, as it is a common culprit. Additionally, checking and repairing any damaged wiring connections can help resolve the issue.

5. Can a DIY enthusiast fix OBDII code B3948 in a 2017 GMC Sierra associated with the left front turn signal circuit?

Depending on your skills and experience, you may be able to address simpler issues like replacing the turn signal bulb or repairing minor wiring damage. For more complex problems, it's recommended to seek professional assistance.

6. Is it safe to continue driving my 2017 GMC Sierra with OBDII code B3948 affecting the left front turn signal circuit?

It is not advisable to drive with a malfunctioning turn signal, as it can compromise your safety and lead to potential traffic violations. Promptly addressing the issue is essential.

7. How much can I expect to pay for repairing OBDII code B3948 in a 2017 GMC Sierra related to the left front turn signal circuit?

The cost of repair can vary depending on the exact cause of the issue and whether you choose to fix it yourself or seek professional help. Costs may range from a simple bulb replacement to more extensive wiring repairs.

8. Can extreme weather conditions affect the occurrence of OBDII code B3948 in a 2017 GMC Sierra's left front turn signal circuit?

Extreme weather conditions like moisture or extreme temperatures can potentially damage the turn signal components or wiring, leading to the triggering of this diagnostic trouble code.

9. Will resetting the OBDII system clear OBDII code B3948 in a 2017 GMC Sierra linked to the left front turn signal circuit?

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

10. Can an intermittent issue trigger OBDII code B3948 in a 2017 GMC Sierra pertaining to the left front turn signal circuit?

Yes, intermittent issues such as loose connections or sporadic wiring faults can trigger this OBDII code. It's important to thoroughly diagnose the problem to pinpoint the exact cause.

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