John Deere 639 – Tailings Master Sensor: CAN Bus Messages Not Received

The Tailings Master Control Unit is not receiving expected CAN Bus messages from other control modules in a timely manner. This loss of communication can result in no noticeable effect, a slow response from the tailings system, or the machine ceasing to operate entirely.

• 9450
• 9540 WTS
• 9550
• 9560
• 9560 STS
• 9640 WTS
• 9650
• 9650 STS
• 9660
• 9660 CTS
• 9660 STS
• 9660 WTS
• 9670
• 9680 WTS
• 9750 STS
• 9760 STS
• 9770
• 9860 STS
• S-Series
• T-Series
• W-Series
• X9-Series

1. 1

   Record all active diagnostic trouble codes from all control units using the machine's display (such as VISIONTRAK™) to identify if other modules are experiencing communication issues

2. 2

   Check system voltage to ensure the battery is fully charged and all battery and ground connections are clean and tight

3. 3

   Visually inspect the wiring harness and connectors associated with the Tailings Master Control Unit and nearby CAN bus components for rubbing, pinching, corrosion, or loose connections

4. 4

   Perform a CAN bus resistance check with power off and batteries disconnected (measure between CAN High and CAN Low pins, often pins C and D; should be approximately 60 ohms. 120 ohms indicates a missing resistor or open circuit, while significantly lower indicates a short or extra resistor)

5. 5

   Perform a key-on voltage check of the CAN wires relative to ground (CAN High, typically a yellow wire, and CAN Low, typically a green wire, should both be approximately 2.5V)

1. 1

   Isolate the fault

   If initial checks do not reveal obvious wiring issues, disconnect other control units on the same CAN bus one by one to see if communication with the Tailings Master Control Unit is restored.

2. 2

   Test terminating resistors

   If the resistance check read 120 ohms (indicating an open circuit or missing resistor) or significantly lower than 60 ohms, locate and test the individual terminating resistors.

3. 3

   Repair wiring and connectors

   Repair any damaged wiring or replace damaged connectors found during the visual inspection. Ensure all connections are clean and secure.

4. 4

   Replace control module

   If all other diagnostic steps have been exhausted and the fault persists, replace the Tailings Master Control Unit.