John Deere 000639.12 – TEC / TEI / PLC: Vehicle CAN BUS Communication Failure

A communication failure has been detected within the Vehicle CAN BUS system, indicating a disruption in critical data exchange between electronic control modules. Depending on the machine series, this fault signifies that the Tractor Electronic Control Unit (TEC) is missing messages, the Tractor Electronic Interface (TEI) is experiencing a message overflow, or there is an internal fault within the Park Lock Controller (PLC). This communication breakdown can severely impair the functionality of the vehicle's systems.

• 9230
• 9330
• 9430
• 9530
• 9630
• 9630T
• 6520
• 6620
• 6820
• 6920
• 6920S

1. 1

   Restart the machine to see if the communication fault clears and normal operation resumes

2. 2

   Conduct a thorough visual inspection of the CAN BUS harness, connectors, and control modules for damage, corrosion, loose connections, or debris

3. 3

   Check for other active or stored fault codes, as multiple simultaneous codes often point to a network-wide communication problem

1. 1

   Perform power-off resistance check

   Turn the vehicle's power completely off. Measure the resistance between the CAN High (Yellow wire) and CAN Low (Green wire) circuits at a convenient connector. A healthy CAN BUS should read approximately 60 Ohms. A reading of 120 Ohms indicates a missing terminating resistor or open circuit. A reading significantly lower than 60 Ohms indicates a short circuit or faulty control unit.

2. 2

   Perform power-on voltage check

   Turn the key to the 'ON' position without starting the engine. Measure DC voltage from CAN High to a clean chassis ground (expected: 2.5 to 3.0 volts) and from CAN Low to chassis ground (expected: 2.0 to 2.5 volts). Voltages outside these ranges indicate a short to power, short to ground, or a faulty transceiver.

3. 3

   Isolate the fault

   If resistance or voltage readings are incorrect, disconnect one control module at a time and re-check the CAN bus readings. If the readings return to normal, the disconnected module is faulty. If disconnecting modules does not correct the readings, the fault lies within the wiring harness (e.g., a short or open circuit between connectors).