BCU 001890.31 – PTO Shaft Spline Identifier Switch Fault. John Deere System Advisory.

BCU 001890.31 (BCU 1890.31)

Code: 001890.31

Shortcode: 1890.31


Error code BCU 001890.31 is triggered when the Basic Control Unit (BCU) of a John Deere vehicle, with the rear PTO unit engaged, detects a change in the rear PTO spline configuration. This diagnostic trouble code can indicate a malfunction or erroneous reading from the PTO shaft spline identifier switch (B179), which is designed to detect and confirm the specific spline configuration engaged on the rear PTO. A fault in this switch could lead to incorrect PTO operation or failure to engage the appropriate implement due to misidentification of the spline setup.


The BCU may respond to this detected fault by issuing a warning alert to the operator and potentially restricting the operation of the rear PTO to prevent incorrect or unsafe implement usage.


  • Inspect PTO Shaft Spline Identifier Switch and Associated Hardware: Check the PTO shaft spline identifier switch (B179) for any signs of physical damage or malfunction. Also, inspect the actual PTO spline for any irregularities or damage that could affect the switch’s ability to accurately identify the spline configuration.
  • Test Switch Functionality: Use diagnostic tools to test the functionality of the spline identifier switch. Verify that it correctly identifies various spline configurations and reacts appropriately when changes are made.
  • Check Wiring and Connections: Examine the wiring and electrical connections for any signs of wear, damage, or loose connections that could impact the switch’s performance. Repair or replace any faulty components.
  • Calibrate or Replace the Switch: If the switch is found to be faulty or not calibrating correctly, recalibrate the device if possible or replace it to ensure accurate identification of the PTO spline.
  • Reset the BCU and Clear Diagnostic Codes: After making any necessary repairs or adjustments, reset the BCU to clear any stored fault codes and ensure the system recognizes the repaired or replaced components.
  • Operational Test: Conduct a full operational test of the rear PTO system to ensure it engages correctly and the spline identifier switch is functioning as expected under various conditions.


Accurate identification of PTO spline configurations is critical for the proper operation of PTO-driven implements. Regular maintenance and timely troubleshooting of the spline identifier switch and related PTO components are essential to maintain the reliability and functionality of your John Deere machinery. This ensures that implements are correctly matched to the tractor’s capabilities, enhancing both safety and efficiency.