AutoCodes – Generic – B3889

B3889 Code - Trailer Brake Lamps

Quick Answer

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. Common causes include Faulty Trailer Brake Lamps, Trailer Brake Lamps harness is open or shorted, Trailer Brake Lamps 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: B3889 indicates Trailer Brake Lamps.
Common causes: Common causes include Faulty Trailer Brake Lamps, Trailer Brake Lamps harness is open or shorted, Trailer Brake Lamps 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 448

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
Tech Notes
Cost to Diagnose
Comments
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Code B3889 Description

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The Body Control Module (BCM) provides a low reference signal and a 5 V reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM applies battery voltage to the center high mounted stop lamp control circuit and Trailer Lighting Control Module. The Trailer Lighting Control Module responds by applying battery voltage to the trailer stop lamp control circuit illuminating the trailer stop lamps.

OBDII Code B3889 - Trailer Brake Lamps - AutoCodes.com — B3889 Code - Trailer Brake Lamps

What does this mean?

What are the Possible Causes of the DTC B3889?

Faulty Trailer Brake Lamps
Trailer Brake Lamps harness is open or shorted
Trailer Brake Lamps circuit poor electrical connection
Faulty Trailer Lighting Control Module

How to Fix the DTC B3889?

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 does this mean?

Code Tech Notes

B3889 02 Trailer Brake Lamps Circuit Short to Ground
B3889 04 Trailer Brake Lamps Circuit Open

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B3889 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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Need Help with the Code?

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Information for Specific Makes

B3889 Buick — Trailer Brake Lamps
B3889 Cadillac — Trailer Brake Lamps
B3889 Chevrolet — Trailer Brake Lamps
B3889 GMC — Trailer Brake Lamps

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.