John Deere 639 – Right Control Unit: CAN Bus Messages Not Received by Right Control Unit

The Right Control Unit is not receiving CAN Bus messages in a timely manner on the J1939 data link. This communication breakdown means the controller has missed expected messages from other modules, which can lead to unpredictable behavior, slow response, or complete loss of function for certain machine systems. Causes include high bus load where devices cannot process messages fast enough, wiring problems, or a faulty controller flooding the network with bad data.

• 9450
• 9550
• 9650
• 9560
• 9660
• 9760
• 9860 STS
• 9860 WTS
• 9540
• 9580
• 9640
• 9680 WTS
• C670
• T550
• T560
• T660
• T670
• W540
• W550
• W650
• W660
• 6230
• 9650 STS
• 9750 STS
• 9400
• 9500
• 9600
• 50 series
• 60 series
• 70 series

1. 1

   Review all active and stored codes to pinpoint the specific message or controller that is the source of the problem

2. 2

   Check for high voltage (fault 627.03 - controller voltage above 16V), which must be resolved first

3. 3

   Visually inspect the CAN bus wiring harness and connectors (e.g., X653 and X654) for damage, rodent damage, chafing, or corrosion around the affected control unit

4. 4

   Check CAN bus resistance with the battery disconnected by measuring between the CAN High and CAN Low pins (often pins C and D on the diagnostic connector). ~60 ohms indicates intact terminating resistors; 120 ohms indicates a missing or damaged resistor

5. 5

   Perform a 'cold boot' by disconnecting power to the affected control unit for 30-60 seconds, or perform a full machine cold boot by disconnecting battery power

1. 1

   Repair wiring or voltage issues

   If diagnostic checks reveal damaged wires, corroded connectors, or a high voltage condition (such as code 627.03), repair these issues first. A simple wire repair often resolves this issue.

2. 2

   Isolate the faulty controller

   If wiring appears intact, unplug controllers from the CAN bus one at a time. If the fault code disappears, the unplugged controller is the source of the problem.

3. 3

   Resolve boot block program error

   If code 628.12 is present (controller cannot exit boot block program), turn the key switch off, wait 30 seconds, and try again. If the condition persists, have a dealer reprogram the control unit with the latest software.

4. 4

   Replace the control unit

   If all other diagnostic steps fail to resolve the issue, or if an internal failure code is present (such as 630.11 failed EEPROM test), replace the affected control unit.