AutoCodes – Buick – B3874 Buick

B3874 Buick Code - Wiper Low Speed Relay Circuit

Quick Answer

The Body Control Module (BCM) controls and monitors the state of the wiper control circuit. Common causes include Faulty Wiper Low Speed Relay, Wiper Low Speed Relay harness is open or shorted, Wiper Low Speed 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: B3874 Buick indicates Wiper Low Speed Relay Circuit.
Common causes: Common causes include Faulty Wiper Low Speed Relay, Wiper Low Speed Relay harness is open or shorted, Wiper Low Speed 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 557

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 B3874 Buick Description

The Body Control Module (BCM) controls and monitors the state of the wiper control circuit. When the windshield wiper switch is placed in to a low speed setting, a signal is applied to the BCM. The BCM then applies the battery positive voltage to the coil side of the relay through the relay control circuit. The Diagnostic Trouble Code (DTC) sets when the ignition is in the ON position or the ignition voltage is between 9-16 volts.

OBDII Code B3874 Buick - Wiper Low Speed Relay Circuit - AutoCodes.com — B3874 Buick Code - Wiper Low Speed Relay Circuit

What does this mean?

What are the Possible Causes of the DTC B3874 Buick?

Faulty Wiper Low Speed Relay
Wiper Low Speed Relay harness is open or shorted
Wiper Low Speed Relay circuit poor electrical connection
Faulty Body Control Module (BCM)

How to Fix the DTC B3874 Buick?

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 B3874 Buick 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.

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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 B3874 Buick Code

1. What does the OBDII code B3874 mean on a Buick?

The B3874 code indicates an issue with the Wiper Low Speed Relay Circuit, which controls the low-speed function of the windshield wipers.

2. What are the common symptoms of code B3874 in a Buick?

Symptoms may include wipers not working on low speed, wipers stuck in one position, or erratic wiper operation.

3. What causes the B3874 code to appear on a Buick?

Common causes include a faulty low-speed wiper relay, damaged wiring or connectors, a malfunctioning wiper motor, or a problem in the Body Control Module (BCM).

4. How is the B3874 code diagnosed?

A mechanic will inspect the wiper relay, wiring, and connectors for damage, test the wiper motor, and use a scan tool to check the BCM for related issues.

5. Can I drive my Buick with the B3874 code active?

While the car may still be drivable, impaired wiper functionality can reduce visibility during rain, making it unsafe to drive in wet conditions.

6. How do you fix the B3874 code on a Buick?

Repairs may involve replacing the low-speed wiper relay, repairing damaged wiring, or replacing the wiper motor if it's faulty.

7. How much does it cost to repair the B3874 code on a Buick?

Repair costs can range from $50 to $300, depending on whether a simple relay replacement or more extensive wiring or motor repairs are needed.

8. Can a failing Body Control Module (BCM) trigger the B3874 code?

Yes, a malfunctioning BCM can cause communication or control issues with the wiper circuit, triggering this code.

9. How can I prevent the B3874 code from recurring?

Regularly inspect and maintain the wiper system, including checking for loose connections, damaged wiring, and ensuring the relay and motor are functioning properly.

10. Do I need a professional to fix the B3874 code on my Buick?

While DIY repairs may be possible for simple fixes like replacing the relay, more complex issues involving wiring or the BCM should be handled by a professional.