John Deere 639.12 – CCU (Chassis Control Unit): Vehicle CAN Bus (500 kBd), High Error Rate

The control unit detects an excessively high number of incorrect or missing CAN Bus messages, indicating a general communication failure or data transfer problem on the vehicle's CAN Bus network.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6090MC
• 6100MC
• 6110MC
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6230R
• 6250R
• 7200R
• 7215R
• 7230R
• 8235R
• 8260R
• 8360R
• 8120T
• 8220T
• 8320T
• 8420T
• 8520T
• 9120-9520 series

1. 1

   Check for accompanying Diagnostic Trouble Codes (DTCs) indicating missing CAN messages from specific modules, as a single failed module can crash the bus

2. 2

   Inspect all CAN bus connections between the CCU and other control modules for signs of damage, loose connections, or corrosion

3. 3

   Visually inspect the main CAN bus wiring harness for chafing, pinch points, or signs of wear that could cause a short to ground or short to power

4. 4

   Test the CAN bus network using a CAN bus analyzer or PC diagnostic tool (like Service ADVISOR) and verify terminating resistors read 60 ohms across CAN High and CAN Low pins with the battery disconnected

5. 5

   Ensure there are no aftermarket electrical devices or damaged components causing electromagnetic interference near the CAN bus network

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical shorts during the repair.

2. 2

   Access the CCU

   Locate the Chassis Control Unit (location varies by model, but often found in the rear cab or under the right-hand console).

3. 3

   Clean and Reseat Connectors

   Disconnect the wiring harness from the CCU. Inspect the pins on both the module and the harness connector. Clean away any corrosion using electrical contact cleaner and ensure the pins are not bent. Reconnect securely.

4. 4

   Repair Wiring

   If the diagnostic checks revealed chafed or broken wires in the CAN bus harness, splice and seal the wires using OEM-approved heat-shrink connectors, or replace the damaged harness section entirely.

5. 5

   Replace Terminating Resistor

   If the CAN network resistance is out of spec (e.g., 120 ohms instead of 60 ohms, indicating a blown resistor), locate and replace the faulty CANBUS terminator.

6. 6

   Replace the CCU

   If the wiring, connectors, and resistors are all in perfect condition but the CCU still fails to communicate on the bus (internal failure), the CCU must be replaced.

7. 7

   Reprogramming

   If a new CCU is installed, reconnect the battery and use John Deere Service ADVISOR to program the new module to the tractor's VIN and calibrate the chassis systems.