AutoCodes – GMC – B3948 2018 GMC Sierra

B3948 2018 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 2018 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 192

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
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Code B3948 2018 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 2018 GMC Sierra - Left Front Turn Signal Circuit - AutoCodes.com — B3948 2018 GMC Sierra Code - Left Front Turn Signal Circuit

What does this mean?

What are the Possible Causes of the DTC B3948 2018 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 2018 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 2018 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 2018 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 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code B3948 on a 2018 GMC Sierra related to the left front turn signal circuit?

The common symptoms include the left front turn signal not working or flashing at a faster rate than usual.

2. What are the possible causes of OBDII code B3948 on a 2018 GMC Sierra for the left front turn signal circuit issue?

Possible causes can include a faulty turn signal bulb, a problem with the wiring or connectors, a defective turn signal switch, or a malfunctioning body control module.

3. How can I diagnose the issue causing OBDII code B3948 on my 2018 GMC Sierra's left front turn signal circuit?

You can start by checking the left front turn signal bulb for any visible damage or a burned-out filament. Next, inspect the wiring and connectors for any signs of damage or corrosion. You may also need to use a multimeter to test for continuity and voltage along the circuit.

4. Is it possible to repair the OBDII code B3948 issue on a 2018 GMC Sierra's left front turn signal circuit myself?

If you have experience working with automotive electrical systems and the necessary tools, you may be able to repair the issue yourself by replacing a faulty bulb, repairing damaged wiring, or fixing loose connectors. However, if you are unsure or uncomfortable with electrical work, it's best to seek professional assistance.

5. Can a malfunctioning body control module cause OBDII code B3948 on a 2018 GMC Sierra's left front turn signal circuit?

Yes, a malfunctioning body control module can potentially cause issues with the left front turn signal circuit and trigger OBDII code B3948. If all other components have been checked and the problem persists, the body control module may need to be diagnosed and replaced if necessary.

6. How do I reset OBDII code B3948 on a 2018 GMC Sierra after repairing the left front turn signal circuit issue?

After repairing the issue causing OBDII code B3948, you can reset the code using an OBDII scanner or by disconnecting the vehicle's battery for a few minutes. Keep in mind that the code may reappear if the underlying problem has not been completely resolved.

7. Can a loose or corroded ground connection cause OBDII code B3948 on a 2018 GMC Sierra's left front turn signal circuit?

Yes, a loose or corroded ground connection can disrupt the electrical flow in the left front turn signal circuit, leading to issues with the turn signal operation and triggering OBDII code B3948. It's important to check and ensure all ground connections are secure and free of corrosion.

8. Are there any specific recalls or technical service bulletins related to OBDII code B3948 on a 2018 GMC Sierra for the left front turn signal circuit?

It's recommended to check with a GMC dealership or the manufacturer's website for any recalls or technical service bulletins related to OBDII code B3948 specifically for the left front turn signal circuit on a 2018 GMC Sierra. These resources may provide additional guidance or information on known issues and solutions.

9. Can a faulty turn signal switch cause OBDII code B3948 on a 2018 GMC Sierra's left front turn signal circuit?

Yes, a faulty turn signal switch can potentially cause issues with the left front turn signal circuit, leading to the triggering of OBDII code B3948. If other components have been checked and the problem persists, the turn signal switch should be inspected and replaced if necessary.

10. How critical is it to address OBDII code B3948 on a 2018 GMC Sierra's left front turn signal circuit promptly?

It is important to address OBDII code B3948 promptly to ensure the proper functioning of the left front turn signal, which is crucial for signaling your intentions to other drivers on the road. Ignoring the issue can compromise safety and may lead to further electrical problems in the vehicle.