AutoCodes – Generic – C1939

C1939 Code - Brake Pressure Switch Input Circuit Failure

Quick Answer

The Anti-Lock Brake System (ABS) Module monitors the Brake Pressure Switch (BPS). Common causes include Faulty Brake Pressure Switch (BPS), Brake Pressure Switch (BPS) harness is open or shorted, Brake Pressure Switch (BPS) 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: C1939 indicates Brake Pressure Switch Input Circuit Failure.
Common causes: Common causes include Faulty Brake Pressure Switch (BPS), Brake Pressure Switch (BPS) harness is open or shorted, Brake Pressure Switch (BPS) 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 15,955

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 Dec 05, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code C1939 Description

The Anti-Lock Brake System (ABS) Module monitors the Brake Pressure Switch (BPS). The ABS Module sets the OBDII code when the Brake Pressure Switch is not to factory specifications.

OBDII Code C1939 - Brake Pressure Switch Input Circuit Failure - AutoCodes.com — C1939 Code - Brake Pressure Switch Input Circuit Failure

What does this mean?

What are the Possible Causes of the DTC C1939?

Faulty Brake Pressure Switch (BPS)
Brake Pressure Switch (BPS) harness is open or shorted
Brake Pressure Switch (BPS) circuit poor electrical connection

How to Fix the DTC C1939?

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 C1939 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 C1939 code?

Need more information on how to fix the C1939 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the C1939 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

C1939 Ford — Brake Pressure Switch Input Circuit Failure
C1939 Lexus — Front Boosted Voltage
C1939 Lincoln — Brake Pressure Switch Input Circuit Failure
C1939 Mercury — Brake Pressure Switch Input Circuit Failure
C1939 Toyota — Front Boosted Voltage

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 C1939 Code

1. What are the common symptoms of OBDII code C1939 (Brake Pressure Switch Input Circuit Failure)?

- Common symptoms include the illumination of the "Brake Warning Light" on the dashboard, issues with the brake system, and potential loss of brake functionality.

2. What are the possible causes of OBDII code C1939?

- The code C1939 can be caused by a faulty brake pressure switch, damaged wiring or connectors in the brake pressure switch circuit, or a malfunctioning brake control module.

3. How serious is the OBDII code C1939 (Brake Pressure Switch Input Circuit Failure)?

- The code C1939 is a serious issue as it directly impacts the proper functioning of the brake system, potentially compromising vehicle safety. It is important to address this code promptly.

4. How can I diagnose OBDII code C1939?

- Diagnosing OBDII code C1939 involves using a diagnostic scanner to retrieve the code, conducting a visual inspection of the brake pressure switch and its wiring, and testing the switch for proper functionality.

5. Is it safe to drive with OBDII code C1939 active?

- It is not recommended to drive with OBDII code C1939 active, as it indicates a potential failure in the brake pressure switch circuit, which can lead to brake-related issues and compromise safety.

6. How can I repair OBDII code C1939?

- Repairing OBDII code C1939 involves replacing the faulty brake pressure switch, repairing or replacing damaged wiring or connectors, and clearing the fault code with a diagnostic scanner.

7. Can I reset OBDII code C1939 without fixing the underlying issue?

- While you can clear the fault code temporarily, it is important to address the underlying issue causing OBDII code C1939 to prevent potential safety hazards and ensure the proper functioning of the brake system.

8. Are there any DIY tips for troubleshooting OBDII code C1939?

- DIY tips for troubleshooting OBDII code C1939 include checking the brake fluid level, inspecting the brake pressure switch for visible damage, and ensuring all brake system components are properly connected.

9. How much does it cost to repair OBDII code C1939 at a mechanic or dealership?

- The cost of repairing OBDII code C1939 can vary depending on the specific cause of the issue, but it generally ranges from $100 to $300 for parts and labor at a mechanic or dealership.

10. Can OBDII code C1939 be prevented?

- While some causes of OBDII code C1939 may be unavoidable, regular maintenance of the brake system, including checking brake fluid levels and inspecting brake components, can help prevent issues that trigger this code.