WOMS
P code powertrain Medium severity

P1820 Transmission Transfer Case Clockwise Shift Relay Coil Circuit Failure

The OBD2 code P1820 indicates a malfunction in the transmission transfer case's clockwise shift relay coil circuit, suggesting a failure in the electrical circuit that controls the relay responsible for shifting the...

Definition

The OBD2 code P1820 indicates a malfunction in the transmission transfer case's clockwise shift relay coil circuit, suggesting a failure in the electrical circuit that controls the relay responsible for shifting the transfer case in a clockwise direction

Common causes

  • Faulty shift relay
  • Damaged wiring or connectors
  • Short circuit in the circuit
  • Open circuit in the circuit
  • Faulty transfer case control module
  • Poor ground connection
  • Corrosion in connectors or terminals
  • Malfunctioning transmission control module

Common misdiagnoses

  • Faulty transfer case
  • Bad shift motor
  • Wiring issues or shorts
  • Faulty transmission control module (TCM)
  • Incorrectly diagnosed transmission fluid issues
  • Malfunctioning vehicle speed sensor
  • Issues with the powertrain control module (PCM)
  • Faulty connectors or terminals
  • Problems with the battery or charging system
  • Misinterpretation of other related codes

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 Wiring and Connectors

    Visually inspect the wiring and connectors associated with the transfer case shift relay. Look for signs of damage, corrosion, or loose connections

  3. 3. Pay special attention to the wiring harness that connects to the relay and the transfer case

  4. 4. Test the Shift Relay

    Locate the transfer case shift relay and test it for proper operation. You can do this by

  5. 5. Removing the relay and using a multimeter to check for continuity

  6. 6. Applying power directly to the relay to see if it activates

  7. 7. Check the Transfer Case Control Module

    If the relay is functioning properly, the issue may lie within the transfer case control module. Check for any signs of damage or malfunction

  8. 8. If possible, perform a reset or reprogramming of the module

  9. 9. Inspect the Transfer Case

    Check the transfer case itself for any mechanical issues or damage that could affect its operation

  10. 10. Ensure that the transfer case is properly lubricated and that there are no leaks

  11. 11. Test the Circuit

    Use a multimeter to test the voltage and ground at the relay connector. Ensure that the circuit is receiving the correct voltage when the vehicle is in the appropriate mode (e.g., 4WD)

  12. 12. Check for any shorts or open circuits in the wiring

  13. 13. Check for Ground Issues

    Ensure that the ground connections for the transfer case and relay are secure and free of corrosion

  14. 14. Consult the Vehicle’s Service Manual

    Refer to the specific service manual for your vehicle for detailed wiring diagrams and troubleshooting procedures related to the transfer case and shift relay

  15. 15. Clear the Code and Test Drive

    After performing any repairs or adjustments, clear the trouble code using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  16. 16. Seek Professional Help

    If the issue persists after following these steps, it may be necessary to consult a professional mechanic or technician who has experience with your specific vehicle make and model. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P1820 code