John Deere 000639.12 – Cab / Armrest Module: Vehicle CAN BUS Fault

Fault code 000639.12 indicates a communication breakdown on the Controller Area Network (CAN) bus, specifically involving the Cab Module or Armrest Module. It is triggered when a control unit's error limit on the CAN bus is exceeded due to a short circuit, open circuit, or excessive data traffic and errors. This results in a loss of communication between modules, which may disable specific machine functions or cause the equipment to default to a neutral state.

• 6R Series Tractors
• 6M Series Tractors
• 6J Series Tractors
• 7R Series Tractors
• 8R Series Tractors
• 8RT Series Tractors
• 9R Series Tractors
• 9RT Series Tractors
• 9RX Series Tractors
• 9030 Series Tractors
• STS Combines
• WTS Combines
• T-series Combines
• W-series Combines
• C-series Combines
• 5430i Sprayers
• 7760 Cotton Pickers

1. 1

   Access the diagnostic menu (e.g., CommandCenter) to record all active and stored fault codes and note their frequency, then clear the codes and operate the machine to identify which codes return.

2. 2

   Visually inspect wiring harnesses connected to the Armrest and Cab control modules for pinched, chafed, corroded, or disconnected wires.

3. 3

   Check battery terminals and alternator for damage, debris, or loose connections.

4. 4

   Inspect fuses related to the reporting control units (e.g., F22 for CAB message, F24 for ECU message).

5. 5

   Perform a CAN Bus resistance test at the 9-pin diagnostic connector with the machine's power completely off and battery disconnected. Measure between Pin C (CAN High) and Pin D (CAN Low). A healthy bus should read approximately 60 Ohms.

6. 6

   If resistance is inconclusive, perform a CAN Bus voltage test with power on (key on, engine off). Measure from CAN High (Pin C) to chassis ground (~2.5V to 2.7V) and CAN Low (Pin D) to chassis ground (~2.3V to 2.5V). Significant deviation indicates a faulty controller or a short to power/ground.

1. 1

   Repair obvious wiring faults

   If visual inspection reveals damaged wiring, loose connections, or corroded terminals on the CAN bus harness, repair or replace the affected sections.

2. 2

   Isolate faulty component via split-half method

   If CAN resistance is incorrect (e.g., 0 Ohms indicating a short, or 120 Ohms indicating an open circuit/missing resistor), systematically unplug control modules one by one. If resistance normalizes when a module is unplugged, that module or its wiring is the fault source.

3. 3

   Test terminating resistors

   If the CAN bus resistance reads ~120 Ohms, locate and test the active and passive terminating resistors at the physical ends of the main CAN bus harness. Each should read 120 Ohms individually. Replace if faulty.

4. 4

   Replace faulty control module

   If a specific module (such as the Armrest Control Unit or Cab Module) is identified as causing a short or communication failure on the bus, replace it with the correct part for your serial number.

5. 5

   Clear codes and verify repair

   After repairs, clear all diagnostic trouble codes, restart the machine, and operate functions to ensure the fault code does not reappear.