BCU 000639.12 – High Error Rate on Vehicle CAN Bus. John Deere System Advisory.

BCU 000639.12 (BCU 639.12)

Code: 000639.12

Shortcode: 639.12


Error code BCU 000639.12 is triggered when the Basic Control Unit (BCU) of a John Deere vehicle detects a high error rate in the Controller Area Network (CAN) Bus messages or identifies a general connectivity problem with the vehicle CAN Bus. This diagnostic trouble code indicates issues such as signal interruptions, corrupted data transfers, or physical connection faults within the CAN Bus network, which could significantly affect vehicle communications and functionality.


Upon detecting excessive errors in the CAN Bus communication, the BCU may issue warnings, potentially limit certain vehicle functionalities, or initiate diagnostic modes to prevent operation under unsafe or unreliable conditions.


  • Inspect CAN Bus Connections: Check all CAN Bus connectors and wiring for signs of damage, corrosion, or looseness. Ensure that all connections are secure and free of physical defects that could disrupt communication.
  • Diagnose Network Traffic: Use specialized diagnostic tools to monitor the CAN Bus network traffic. Look for patterns or sources of errors that could indicate where the problems are originating.
  • Resolve Electrical Interference: Identify and mitigate any potential sources of electrical interference that could be affecting CAN Bus signal integrity. This may involve rerouting wires, shielding cables, or addressing other electronic device interferences.
  • Update Software and Firmware: Make sure that all control units on the CAN Bus are running the latest software and firmware versions. Updates may resolve bugs or compatibility issues that could be contributing to the high error rate.
  • Replace Faulty Components: If specific components of the CAN Bus system are found to be faulty, replace them to restore proper communication and reduce error rates.
  • Clear Errors and Test System: After making any repairs or updates, clear the error codes from the BCU and conduct thorough testing under various operating conditions to ensure that the error rate has normalized and communications are stable.


The CAN Bus is critical for the integration and reliable operation of various vehicle systems. Maintaining its integrity is crucial for the overall performance and safety of John Deere machinery. Regular monitoring and timely maintenance of the CAN Bus can prevent communication issues and ensure seamless operation across all connected systems.