AutoCodes – Generic – B3840

B3840 Code - Park Lamp Signal Circuit Low

Quick Answer

The Body Control Module (BCM) monitors the activity of the park lamp relay switch with the headlamp switch in either the PARK position or the HEAD position. Common causes include Faulty Park Lamp Relay, Park Lamp Relay harness is open or shorted, Park Lamp Relay 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: B3840 indicates Park Lamp Signal Circuit Low.
Common causes: Common causes include Faulty Park Lamp Relay, Park Lamp Relay harness is open or shorted, Park Lamp Relay 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 1,656

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 Mar 23, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code B3840 Description

The Body Control Module (BCM) monitors the activity of the park lamp relay switch with the headlamp switch in either the PARK position or the HEAD position. The Diagnostic Trouble Code (DTC) sets when the BCM detects an open or a short to ground in the park lamp supply voltage circuit with the headlamp switch in either the PARK position or the HEAD position.

OBDII Code B3840 - Park Lamp Signal Circuit Low - AutoCodes.com — B3840 Code - Park Lamp Signal Circuit Low

What does this mean?

What are the Possible Causes of the DTC B3840?

Faulty Park Lamp Relay
Park Lamp Relay harness is open or shorted
Park Lamp Relay circuit poor electrical connection
Faulty Body Control Module (BCM)

How to Fix the DTC B3840?

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 B3840 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 B3840 code?

Need more information on how to fix the B3840 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the B3840 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

B3840 Buick — Park Lamp Signal Circuit Low
B3840 Cadillac — Park Lamp Signal Circuit Low
B3840 Chevrolet — Park Lamp Signal Circuit Low
B3840 GMC — Park Lamp Signal Circuit Low
B3840 Pontiac — Park Lamp Signal Circuit Low
B3840 Saturn — Park Lamp Signal Circuit Low

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 B3840 Code

1. What are the common symptoms of OBDII code B3840 (Park Lamp Signal Circuit Low)?

- Common symptoms include dim or non-functional park lamps, issues with turn signal operation, and the illumination of the Check Engine light.

2. What are the typical causes of OBDII code B3840?

- The code B3840 is usually caused by a faulty park lamp signal circuit, a malfunctioning park lamp switch, wiring issues, or a defective body control module.

3. How can I diagnose the OBDII code B3840?

- Diagnosing the code B3840 involves inspecting the park lamp signal circuit for damage, checking the park lamp switch for proper operation, and using a diagnostic scanner to retrieve trouble codes.

4. Can I still drive my vehicle with OBDII code B3840?

- While the vehicle may still be operational with code B3840, it is recommended to address the issue promptly to ensure proper lighting functionality for safety reasons.

5. How do I repair OBDII code B3840?

- Repairing code B3840 may involve repairing or replacing damaged wiring, replacing the park lamp switch, or addressing any underlying issues with the body control module.

6. Are there any DIY tips for fixing OBDII code B3840?

- DIY tips include checking and cleaning the park lamp connectors, inspecting the wiring for any visible damage, and ensuring all connections are secure and free of corrosion.

7. Is it safe to reset the OBDII code B3840 without fixing the underlying issue?

- It is not recommended to reset the code without addressing the underlying problem, as it may lead to continued lighting issues and potential safety hazards.

8. Can extreme weather conditions trigger OBDII code B3840?

- Yes, extreme weather conditions such as heavy rain or snow can potentially cause electrical issues that trigger code B3840 due to water damage or corrosion.

9. How long does it typically take to repair OBDII code B3840?

- The repair time for code B3840 can vary depending on the exact cause and the extent of the issue, but it may take anywhere from 1-3 hours for a professional technician to diagnose and repair.

10. Will fixing OBDII code B3840 affect my vehicle's performance?

- Fixing code B3840 is primarily related to the lighting system and should not have a direct impact on the vehicle's overall performance, but it is essential for safety and compliance with regulations.