WOMS
C code chassis High severity

C1939 Brake Pressure Switch Input Circuit Failure

The OBD2 code C1939 indicates a malfunction in the brake pressure switch input circuit, which may affect the vehicle's braking system and related safety features

Definition

The OBD2 code C1939 indicates a malfunction in the brake pressure switch input circuit, which may affect the vehicle's braking system and related safety features

Common causes

  • Faulty brake pressure switch
  • Damaged wiring or connectors
  • Short circuit in the brake pressure switch circuit
  • Open circuit in the brake pressure switch circuit
  • Corrosion or poor connections at the switch or connectors
  • Malfunctioning brake control module
  • Low brake fluid level
  • Air in the brake lines

Common misdiagnoses

  • Faulty brake pressure switch
  • Wiring issues or shorts in the brake pressure switch circuit
  • ABS module failure
  • Brake fluid level sensor malfunction
  • Faulty brake master cylinder
  • Issues with the brake pedal position sensor
  • Problems with the vehicle's electronic control unit (ECU)

Troubleshooting steps

  1. 1. Check the OBD-II Scanner

    Ensure that the code is not a false reading. Clear the code and see if it returns after a short drive

  2. 2. Inspect the Brake Pressure Switch

  3. 3. Locate the brake pressure switch, which is usually found near the brake master cylinder

  4. 4. Check for any visible damage, corrosion, or leaks around the switch

  5. 5. Test the Brake Pressure Switch

  6. 6. Use a multimeter to test the switch. It should show continuity when the brake pedal is pressed and no continuity when released

  7. 7. If the switch is faulty, replace it

  8. 8. Examine Wiring and Connectors

  9. 9. Inspect the wiring harness and connectors leading to the brake pressure switch for any signs of damage, fraying, or corrosion

  10. 10. Ensure that all connections are secure and free of dirt or moisture

  11. 11. Check for Short Circuits

  12. 12. Use a multimeter to check for shorts in the wiring. Look for continuity between the brake pressure switch circuit and ground or other circuits

  13. 13. Inspect the Brake System

  14. 14. Ensure that the brake fluid level is adequate and that there are no leaks in the brake system

  15. 15. Check the brake master cylinder and brake lines for any issues that could affect brake pressure

  16. 16. Scan for Additional Codes

  17. 17. Check for any other related trouble codes that may provide more context to the issue. Sometimes, multiple codes can point to a common problem

  18. 18. Test the Brake System

  19. 19. If applicable, perform a brake system pressure test to ensure that the system is functioning correctly

  20. 20. Consult the Vehicle’s Service Manual

  21. 21. Refer to the specific service manual for your vehicle for any manufacturer-specific troubleshooting steps or specifications

  22. 22. Seek Professional Help

  23. 23. If the issue persists after performing these steps, consider consulting a professional mechanic or technician who has experience with your vehicle make and model. By following these steps, you should be able to identify and resolve the issue related to the C1939 code