Case IH F-639-02 - ECU – ECU: CAN A Bus Off Passive Failure

The Engine Control Unit (ECU) has detected a critical communication failure on the CAN A network. The ECU is unable to send or receive messages because the network status has been forced into a 'Bus Off' (passive) state. This is typically caused by a physical layer issue, such as a broken wire, a short circuit, a missing terminating resistor, or a failed module pulling the network voltage out of its target range.

• MAGNUM AFS Connect
• Magnum 180
• Magnum 200
• Magnum 240
• Magnum 340
• Magnum 380
• Magnum 400 AFS Connect
• Steiger 370
• Steiger 420
• Steiger 500
• Steiger 620
• 240 Series Axial-Flow Combines
• 1021F Wheel Loader
• 1121F Wheel Loader
• 721F Wheel Loader
• 1150K Crawler Dozer
• 1650L Crawler Dozer
• Backhoe Loaders

1. 1

   Turn the key switch to the OFF position.

2. 2

   Use a multimeter to measure the resistance of the CAN connection on the vehicle harness side (across the CAN High and CAN Low pins).

3. 3

   Interpret resistance readings: approximately 60 ohms is healthy, 120 ohms indicates a missing/faulty terminating resistor or open circuit, and Open (infinite resistance) indicates damaged wiring or a disconnected connector.

4. 4

   Check the CAN A lines for short circuits to ground or short circuits to battery voltage.

1. 1

   Disconnect Power

   Disconnect the battery to prevent electrical spikes while working on the harness.

2. 2

   Inspect Wiring

   Trace the CAN A bus wiring harness from the ECU. Look for chafed wires, melted insulation, or corrosion at the connectors.

3. 3

   Repair Wiring/Connectors

   Repair any broken wires or replace damaged connector pins. Ensure all connections are tight and free of moisture.

4. 4

   Replace Terminating Resistor

   If the resistance check yielded 120 ohms and the wiring is intact, locate the external CAN terminating resistor on the harness and replace it. (Note: The ECU usually contains one internal terminating resistor, while the other is external on the harness).

5. 5

   ECU Verification

   If the wiring is perfect and the external resistor is good, the ECU's internal CAN transceiver may have failed. In this case, the ECU will need to be repaired by a specialist or replaced.

6. 6

   Clear Codes

   Reconnect the battery, turn the key ON, and use the electronic service tool to clear the inactive F-639-02 code.