WOMS
P code powertrain Medium severity

P1890 Transmission 4WD Mode Select Return Input Circuit Failure

The OBD2 code P1890 indicates a failure in the transmission's 4WD mode select return input circuit, which means there is a problem with the electrical signal or connection related to the selection of the four-wheel...

Definition

The OBD2 code P1890 indicates a failure in the transmission's 4WD mode select return input circuit, which means there is a problem with the electrical signal or connection related to the selection of the four-wheel drive mode

Common causes

  • Faulty mode select switch
  • Damaged wiring or connectors
  • Short circuit in the circuit
  • Open circuit in the circuit
  • Faulty transmission control module (TCM)
  • Corroded terminals
  • Poor ground connection
  • Malfunctioning transfer case control module

Common misdiagnoses

  • Faulty transmission control module (TCM)
  • Defective transfer case motor
  • Wiring issues or shorts in the circuit
  • Malfunctioning 4WD switch
  • Faulty vehicle speed sensor (VSS)
  • Incorrectly diagnosed transmission problems
  • Issues with the powertrain control module (PCM)
  • Low transmission fluid levels or contamination
  • Problems with the transfer case itself
  • Misinterpretation of other related codes

Troubleshooting steps

  1. 1. 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 multiple issues

  2. 2. Inspect Wiring and Connectors

    Visually inspect the wiring and connectors associated with the 4WD mode select switch and the transmission control module. Look for

  3. 3. Damaged, frayed, or corroded wires

  4. 4. Loose or corroded connectors

  5. 5. Repair or replace any damaged components as necessary

  6. 6. Test the 4WD Mode Select Switch

    The mode select switch may be faulty. Test the switch for proper operation using a multimeter

  7. 7. Check for continuity in each position of the switch

  8. 8. Ensure that the switch is sending the correct signals to the transmission control module

  9. 9. Check the Transmission Control Module (TCM)

    Inspect the TCM for any signs of damage or corrosion

  10. 10. If possible, test the TCM to ensure it is functioning correctly. This may require specialized equipment or professional assistance

  11. 11. Inspect the Transfer Case

    If applicable, check the transfer case for proper operation. Ensure that it is engaging and disengaging correctly

  12. 12. Look for any signs of mechanical failure or fluid leaks

  13. 13. Check for Ground Issues

    Ensure that all ground connections related to the 4WD system and TCM are secure and free of corrosion. Poor grounding can lead to erratic behavior and fault codes

  14. 14. Perform a System Reset

    After addressing any issues found, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  15. 15. Consult the Service Manual

    Refer to the vehicle’s service manual for specific diagnostic procedures and specifications related to the 4WD system and the P1890 code

  16. 16. Seek Professional Help

    If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who specializes in transmission and 4WD systems.Additional Notes: - Always ensure that the vehicle is safely secured and that you follow proper safety protocols when working on automotive systems. - Keep in mind that the specific troubleshooting steps may vary depending on the make and model of the vehicle, so always refer to the manufacturer’s guidelines when available