BCU 523921.09 – E11/2 /E31R Worklights on Rear of Roof, Incorrect CAN BUS Message. John Deere System Advisory.

BCU 523921.09 (BCU )

Code: 523921.09



Diagnostic trouble code BCU 523921.09 is triggered when there is a communication issue between the power module PC0 and the Basic Control Unit (BCU) concerning the worklights on the rear of the roof (either E11/2 or E31R). The problem involves intermittent or nonexistent reception of one or more CAN (Controller Area Network) messages from the BCU to power module PC0. This communication error may be caused by loose wiring, connectivity issues, or faults within the CAN BUS system itself, which could impact the proper operation of the worklights.


This communication error may lead to improper functioning of the rear roof worklights, such as failing to turn on or off according to the operator’s commands. The system may alert the operator to this issue through diagnostic displays or warning lights.


  • Inspect CAN Bus Connections: Thoroughly check all CAN bus connections between the BCU and power module PC0. Ensure that they are secure and free from corrosion or damage.
  • Test Wire Continuity and Security: Use diagnostic tools to test the continuity of the wires involved in the CAN bus system. Focus on identifying any loose or intermittent connections that could be disrupting communication.
  • Resolve Connectivity Issues: Tighten or replace any loose or damaged connectors or wiring found during the inspection.
  • Check for CAN Bus Interference: Ensure that there is no electromagnetic interference affecting CAN bus communication. Keep wiring away from high voltage lines or equipment that may emit strong electromagnetic fields.
  • Reset and Reconfigure Systems: After ensuring all physical connections are intact and secure, reset the CAN bus system and reconfigure settings if necessary to ensure proper communication protocols are followed.
  • Monitor System Performance: Continuously monitor the system to ensure that communication has been fully restored and that no further message errors are occurring.


Maintaining clear and precise communication in vehicle control systems is crucial for operational reliability. Regular system checks and updates of the system configurations and CAN BUS protocols are necessary to prevent communication errors and ensure that each component functions correctly as part of the overall system architecture. Addressing these issues promptly helps maintain the operational efficiency and safety of the equipment.

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