AutoCodes – GMC – B3948 2016 GMC Sierra

B3948 2016 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 2016 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.

Save to My Repairs My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 161

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
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code B3948 2016 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 2016 GMC Sierra - Left Front Turn Signal Circuit - AutoCodes.com — B3948 2016 GMC Sierra Code - Left Front Turn Signal Circuit

What does this mean?

What are the Possible Causes of the DTC B3948 2016 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 2016 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 2016 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 2016 GMC Sierra code?

Need more information on how to fix the B3948 2016 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the B3948 2016 GMC Sierra code diagnosed by a professional: Find a repair shop in your area

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 2016 GMC Sierra Code

1. What does the OBDII code B3948 mean on a 2016 GMC Sierra?

The B3948 code indicates an issue with the Left Front Turn Signal Circuit, such as a malfunction or fault in the wiring, bulb, or related components.

2. What are the common symptoms of the B3948 code on a GMC Sierra?

Symptoms may include the left front turn signal not working, rapid flashing of the turn signal indicator, or a warning on the dashboard.

3. What causes the B3948 code to appear on a 2016 GMC Sierra?

Common causes include a burnt-out turn signal bulb, damaged wiring or connectors, a faulty turn signal socket, or a problem with the body control module (BCM).

4. How do I fix the B3948 code on my GMC Sierra?

Start by inspecting and replacing the left front turn signal bulb if itâ€™s burnt out. Check the wiring and connectors for damage or corrosion, and replace or repair as necessary. If the issue persists, the BCM may need further diagnostic testing.

5. Can a blown fuse cause the B3948 code on a 2016 GMC Sierra?

Yes, a blown fuse in the turn signal circuit can cause this code. Check the fuse panel and replace any blown fuses related to the turn signal system.

6. How can I check if the left front turn signal bulb is the issue for the B3948 code?

Remove the bulb and visually inspect it for damage or burn marks. You can also test it with a multimeter or replace it with a new bulb to see if the issue is resolved.

7. Will the B3948 code cause other electrical problems in my GMC Sierra?

This code is specific to the left front turn signal circuit, but unresolved issues like shorted wiring could potentially affect other electrical components if left unaddressed.

8. Can I drive my 2016 GMC Sierra with the B3948 code?

While the vehicle may still be drivable, it is unsafe to drive without a functioning turn signal. Address the issue promptly to ensure proper signaling.

9. How do I reset the B3948 code on a GMC Sierra after repairs?

After fixing the issue, you can reset the code using an OBDII scanner. If the problem is resolved, the code should not reappear.

10. What tools are needed to diagnose the B3948 code on a 2016 GMC Sierra?

You may need a multimeter to test electrical connections, a replacement bulb, basic hand tools for bulb or socket removal, and an OBDII scanner to diagnose and clear the code.