BCU 000115.31 – Alternator Malfunction Warning. John Deere System Advisory.

BCU 000115.31 (BCU 115.31)

Code: 000115.31

Shortcode: 115.31


Error code BCU 000115.31 indicates a malfunction in the alternator, specifically within the preexcitation circuit, which is identified when the Basic Control Unit (BCU) detects an open circuit. This malfunction can impact the alternator’s ability to charge the battery, leading to inadequate electrical power for the vehicle’s systems and potential battery drain.


The BCU may respond to this alternator issue by activating a warning light on the dashboard to alert the operator of the charging system’s failure, potentially preventing the vehicle from maintaining adequate electrical power.


  • Inspect Alternator Wiring and Connections: Check the wiring and connections associated with the alternator, particularly focusing on the preexcitation circuit. Look for any signs of wear, damage, or disconnections that could be causing the open circuit.
  • Test Alternator Functionality: Perform a complete diagnostic test on the alternator to assess its functionality. Use a multimeter to check for proper voltage output and continuity in the preexcitation circuit.
  • Repair or Replace Faulty Components: If any damaged wiring or connectors are found, repair or replace them. If the alternator itself is found to be faulty and unable to be repaired, it may need to be replaced.
  • Verify System Performance: After repairs or replacement, verify that the charging system is functioning correctly by checking the battery voltage with the engine running and ensuring it is within the manufacturer’s specifications.
  • Reset the BCU: Clear any fault codes from the BCU and perform a final system check to ensure no further electrical issues are present and the code does not reappear.


The alternator is crucial for providing the electrical energy necessary for all vehicle operations and maintaining battery charge. Regular checks of the alternator and charging system are vital to prevent unexpected vehicle downtime and ensure consistent performance. Addressing issues promptly when they are detected can help maintain the longevity and reliability of your John Deere equipment.