WOMS
P code powertrain High severity

P1840 Transmission Transfer Case Shift Motor Short Circuit To Battery

The OBD2 code P1840 indicates a short circuit in the transmission transfer case shift motor, which is causing an electrical fault by connecting directly to the battery

Definition

The OBD2 code P1840 indicates a short circuit in the transmission transfer case shift motor, which is causing an electrical fault by connecting directly to the battery

Common causes

  • Shorted wiring or connectors
  • Faulty transfer case shift motor
  • Damaged or corroded electrical connections
  • Malfunctioning control module
  • Grounding issues
  • Water intrusion or moisture in electrical components

Common misdiagnoses

  • Faulty transfer case shift motor
  • Wiring harness issues
  • Faulty transmission control module (TCM)
  • Bad ground connections
  • Faulty transfer case control module
  • Low transmission fluid levels
  • Faulty sensors related to the transfer case
  • Incorrectly diagnosed electrical issues

Troubleshooting steps

  1. 1. Visual Inspection

    Wiring and Connectors: Inspect the wiring harness and connectors leading to the transfer case shift motor for any signs of damage, fraying, or corrosion. Look for loose connections or exposed wires that could cause a short circuit

  2. 2. Shift Motor

    Check the shift motor itself for any physical damage or signs of wear

  3. 3. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. This can provide more context and help identify if there are other issues affecting the system

  4. 4. Test the Shift Motor

    Resistance Test: Disconnect the shift motor connector and use a multimeter to measure the resistance across the motor terminals. Compare the readings to the manufacturer's specifications

  5. 5. Power and Ground

    With the connector still disconnected, check for power and ground at the connector while operating the vehicle's 4WD system. Ensure that the correct voltage is present

  6. 6. Inspect the Transfer Case Control Module

    If applicable, check the transfer case control module for any signs of damage or corrosion. Ensure that it is functioning properly and that there are no issues with its connections

  7. 7. Check Fuses and Relays

    Inspect the fuses and relays associated with the transfer case and shift motor. Replace any blown fuses and test the relays to ensure they are functioning correctly

  8. 8. Perform a Continuity Test

    With the shift motor disconnected, perform a continuity test on the wiring harness to ensure there are no shorts to ground or battery voltage. This can help identify any damaged wires

  9. 9. Check for Ground Issues

    Ensure that the ground connections for the shift motor and control module are secure and free of corrosion. A poor ground can lead to erratic behavior and false codes

  10. 10. Clear Codes and Test Drive

    After performing the above checks and making any necessary repairs, clear the trouble codes using the OBD-II scanner. Take the vehicle for a test drive to see if the code reappears

  11. 11. Seek Professional Help

    If you are unable to resolve the issue after following these steps, it may be best 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 P1840 code