AutoCodes – GMC – B3948 GMC

B3948 GMC 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 GMC 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 1,914

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 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 an open/high resistance in the left front turn signal control circuit.

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

What does this mean?

What are the Possible Causes of the DTC B3948 GMC?

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 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 is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B3948 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 B3948 GMC code?

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Need Help with the Code?

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

Information for Specific GMC Models

B3948 2014 GMC Sierra — Left Front Turn Signal Circuit
B3948 2015 GMC Sierra — Left Front Turn Signal Circuit
B3948 2016 GMC Sierra — Left Front Turn Signal Circuit
B3948 2017 GMC Sierra — Left Front Turn Signal Circuit
B3948 2018 GMC Sierra — Left Front 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 B3948 GMC Code

1. What are common symptoms of OBDII code B3948 GMC related to the Left Front Turn Signal Circuit?

- Common symptoms include the left front turn signal not working, rapid blinking, or the turn signal staying on constantly.

2. What are the possible causes of OBDII code B3948 GMC indicating an issue with the Left Front Turn Signal Circuit?

- Possible causes include a faulty turn signal bulb, a damaged wiring harness, a malfunctioning turn signal switch, or a problem with the body control module.

3. How can I diagnose the OBDII code B3948 GMC for the Left Front Turn Signal Circuit issue?

- You can start by visually inspecting the left front turn signal bulb and its socket, checking the wiring for any damage, and testing the turn signal switch and body control module using a multimeter.

4. What are some repair tips for addressing OBDII code B3948 GMC related to the Left Front Turn Signal Circuit?

- Repair tips may include replacing the faulty turn signal bulb, repairing or replacing damaged wiring, replacing the turn signal switch if needed, or reprogramming the body control module.

5. Can a DIY enthusiast fix OBDII code B3948 GMC associated with the Left Front Turn Signal Circuit?

- Depending on the specific issue, DIY enthusiasts with some experience in automotive repair may be able to address this code by following repair guides and using basic tools.

6. Is it safe to drive with OBDII code B3948 GMC triggered by a problem in the Left Front Turn Signal Circuit?

- It is not recommended to drive with a malfunctioning turn signal, as it can pose a safety hazard by affecting your ability to signal your intentions to other drivers on the road.

7. How much does it typically cost to repair OBDII code B3948 GMC due to the Left Front Turn Signal Circuit issue?

- The cost of repair can vary depending on the underlying cause, but it may range from a few dollars for a replacement bulb to a few hundred dollars for more complex repairs involving wiring or modules.

8. Are there any recalls or technical service bulletins related to OBDII code B3948 GMC for the Left Front Turn Signal Circuit?

- It's recommended to check with the manufacturer or a dealership to see if there are any recalls or technical service bulletins related to this specific OBDII code and issue.

9. What are the consequences of ignoring OBDII code B3948 GMC indicating a problem with the Left Front Turn Signal Circuit?

- Ignoring this code can lead to potential safety risks on the road, reduced visibility for other drivers, and potential legal consequences if you are pulled over for not having functioning turn signals.

10. How can I prevent OBDII code B3948 GMC from recurring in the future after fixing the Left Front Turn Signal Circuit issue?

- To prevent this code from recurring, it's important to perform regular maintenance checks on your turn signal system, including inspecting and replacing bulbs, checking wiring, and addressing any issues promptly.