WOMS
P code powertrain Medium severity

P0812 Reverse Input Circuit

The OBD2 code P0812 indicates a malfunction in the reverse input circuit, which typically means there is an issue with the signal that detects when the vehicle is in reverse gear

Definition

The OBD2 code P0812 indicates a malfunction in the reverse input circuit, which typically means there is an issue with the signal that detects when the vehicle is in reverse gear

Common causes

  • Faulty transmission range sensor
  • Damaged wiring or connectors in the reverse input circuit
  • Malfunctioning transmission control module (TCM)
  • Low transmission fluid level
  • Faulty neutral safety switch
  • Corroded or loose electrical connections
  • Internal transmission issues

Common misdiagnoses

  • Transmission control module (TCM) failure
  • Faulty transmission range sensor
  • Wiring issues or shorts in the reverse input circuit
  • Defective neutral safety switch
  • Malfunctioning transmission solenoids
  • Incorrectly diagnosed transmission problems
  • Battery or electrical system issues affecting the TCM
  • Software or calibration issues in the TCM

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context and help identify related issues

  2. 2. Inspect the Reverse Switch

    Locate the reverse switch (usually found on the transmission) and inspect it for any physical damage or wear

  3. 3. Ensure that the switch is properly connected and that the wiring harness is intact

  4. 4. Test the Reverse Switch

    Use a multimeter to test the reverse switch for continuity. When the switch is activated (in reverse), it should show continuity

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

  6. 6. Check Wiring and Connectors

    Inspect the wiring and connectors leading to the reverse switch for any signs of damage, corrosion, or loose connections

  7. 7. Repair or replace any damaged wiring or connectors

  8. 8. Inspect the Transmission Control Module (TCM)

    Check the TCM for any signs of damage or corrosion. Ensure that it is securely connected

  9. 9. If necessary, test the TCM for proper operation. This may require specialized equipment or professional assistance

  10. 10. Check for Ground Issues

    Ensure that the ground connections related to the transmission and reverse switch are secure and free of corrosion

  11. 11. A poor ground can lead to erratic signals and trigger the P0812 code

  12. 12. Look for Mechanical Issues

    Inspect the transmission for any mechanical issues that could affect the reverse gear operation

  13. 13. Ensure that the transmission is functioning properly and that there are no internal problems

  14. 14. Clear the Code and Test Drive

    After performing the necessary repairs, clear the trouble codes using the OBD-II scanner

  15. 15. Take the vehicle for a test drive to see if the code reappears. Monitor the transmission operation to ensure it is functioning correctly

  16. 16. Consult a Professional

    If the code persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who has experience with transmission issues and can perform more advanced diagnostics. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P0812 code. Always refer to the vehicle's service manual for specific procedures and specifications related to your make and model