Case IH 3652 (DTC 911B) - ECU – Engine Control Unit (ECU): CAN A Bus off passive failure

The ECU has detected an excessive number of communication errors on the CAN A (or CAN 1) bus. To prevent disrupting the entire network with corrupted data, the ECU enters a "bus off passive" state, effectively dropping its communication with the main vehicle controller.

• MAXXUM T4E
• 240 Series Axial-Flow Combines
• Magnum Series Tractors (180, 200, 240, 280, 310, 340, 380)
• Steiger Series Tractors (370, 420, 470, 500, 620)
• Puma and Optum Series Tractors
• Case IH Construction Equipment (Wheel Loaders, Crawler Dozers, Backhoes)

1. 1

   Visually inspect the CAN bus wiring harness between the ECU and the vehicle controllers for chafed wires, cuts, or corrosion. Pay special attention to the ECU connector pins.

2. 2

   With the battery disconnected, perform a resistance test on the CAN bus circuit. A healthy CAN bus with two 120-ohm resistors in parallel should read approximately 60 ohms. Individual resistors should read 108 - 132 ohms.

3. 3

   Check the ECU internal terminating resistor by using a multimeter to measure the resistance directly at the ECU connector pins designated for the CAN circuit.

4. 4

   If wiring and terminators are intact, perform module isolation by disconnecting other modules on the network one by one to see if CAN communication is restored (identifying another faulty module pulling bus voltage down).

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery before servicing the electrical system.

2. 2

   Repair Wiring

   If the diagnostic checks revealed damaged wiring, repair the harness using approved temporary splicing methods or replace the affected harness section entirely to prevent moisture intrusion.

3. 3

   Replace Terminating Resistors

   If a CAN bus terminator tests out of specification (open or shorted), locate the faulty terminator (typically found at the ends of the CAN circuit, such as under the air filter or behind the controllers) and plug in a new termination module.

4. 4

   Replace the ECU

   If the wiring harness is completely intact, the external terminators are good, and the ECU's internal CAN transceiver or internal resistor has failed, the Engine Control Unit must be replaced.

5. 5

   Clear Codes and Test

   Reconnect the battery, turn the key on, and use the Electronic Service Tool (EST) to clear the fault codes. Start the engine and verify that CAN communication is restored and the code does not return.