BCU 523689.31 – S22 Differential Lock Switch Fault. John Deere System Advisory.

BCU 523689.31 (BCU )

Code: 523689.31



Error code BCU 523689.31 is triggered when the Basic Control Unit (BCU) of a John Deere vehicle detects an engage signal from the differential lock switch that persists for more than 15 seconds. This diagnostic trouble code suggests a potential issue with the switch itself, such as a stuck button or a fault in the switch circuitry, which may cause the differential lock to remain engaged unintentionally or signal erroneously.


The continuous engage signal might lead the system to either keep the differential lock engaged longer than intended or issue a warning. This could potentially affect the drivability and maneuverability of the vehicle, especially under conditions where differential lock should not be engaged.


  • Inspect the Differential Lock Switch: Check the switch for any physical damage, debris, or wear that might cause it to stick or malfunction. Ensure that the switch returns to its neutral position after being pressed.
  • Test Electrical Connections: Examine the wiring and connectors associated with the differential lock switch for signs of corrosion, loose connections, or damage that might be causing continuous signal transmission.
  • Measure Signal Continuity: Use a multimeter to test the continuity and electrical behavior of the switch. This can help determine if the switch is faulty or if the issue lies elsewhere in the circuit.
  • Replace Faulty Switch: If the switch is found to be defective, replace it to ensure proper functionality. A new switch should correct the issue of prolonged engagement signaling.
  • Reset the BCU and Clear Diagnostic Codes: After replacing the switch and ensuring all connections are secure, reset the BCU to clear the error code and reinitialize the system. This ensures the system recognizes the new component and operates correctly.
  • Perform Operational Test: Test the vehicle to ensure that the differential lock operates correctly and disengages when the switch is released. Monitor the system to ensure no further fault codes are generated.
  • Documentation and Monitoring: Document the repair and monitor the differential lock function over time to ensure no recurring issues. This can help in early detection if the problem arises again.


Regular maintenance and checks of the vehicle’s control systems, especially those involved in operational safety and performance like the differential lock, are crucial. Keeping these systems in good working order ensures the vehicle operates safely and efficiently, preventing issues that could arise from faulty equipment.