Case IH 3870 – Engine Control Unit (ECU / ECM): CAN communication failure between vehicle controller and ECU - BC2ECU1 message

The Engine Control Unit (ECU) is not receiving the expected periodic data messages from the Vehicle Controller over the Controller Area Network (CAN) bus, pointing to an open circuit, a shorted CAN bus, a failed terminating resistor, or a malfunctioning controller.

• Steiger T4B
• 240 Series Axial-Flow Combines
• Steiger
• Magnum (Series 4)
• Maxxum
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Check for accompanying codes (e.g., DTC 93CB, 951B, or 3277) to determine if multiple modules are reporting communication timeouts, indicating the entire CAN bus is down.

2. 2

   Verify the tractor battery voltage is within normal operating range and ensure no external power supply is connected that could cause voltage spikes.

3. 3

   Check ECU supply voltage with the ignition switch in the ON position (e.g., check the ECU A-095 supply voltage at the harness connector).

4. 4

   Visually inspect the CAN bus wiring harness for chafed, cut, or corroded wires, particularly where routed under the cab or connected to the ECU.

5. 5

   Test CAN bus resistance with the battery disconnected by measuring across the CAN High and CAN Low pins. A healthy bus reads ~60 ohms. 120 ohms indicates a missing/failed terminating resistor. Out of limits indicates an open circuit.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the machine's battery to prevent electrical damage during testing.

2. 2

   Isolate the Harness

   Locate the CAN bus wiring harness connecting the Vehicle Controller to the Engine ECU.

3. 3

   Inspect and Clean Connectors

   Disconnect the harness at both the ECU and the Vehicle Controller. Inspect for pushed-out pins, moisture, or corrosion. Clean the contacts with electrical contact cleaner and apply dielectric grease if necessary.

4. 4

   Repair Wiring

   If continuity testing reveals a break or short to ground in the CAN High or CAN Low wires, repair the damaged section of the harness or replace the harness entirely.

5. 5

   Replace Terminating Resistors

   If the CAN bus resistance measured 120 ohms during diagnostics, locate the faulty CAN bus terminating resistor (often located near the ECU or under the cab) and replace it.

6. 6

   Module Isolation Test

   If the wiring and resistors are intact, a faulty module may be pulling the CAN bus down. Disconnect controllers on the network one individually until communication is restored to the instrument cluster/diagnostic tool.

7. 7

   Replace Faulty Module

   If the ECU or Vehicle Controller is found to be internally shorted, replace the module.

8. 8

   Clear Codes

   Reconnect the battery, turn the ignition ON, and use the Case IH Electronic Service Tool (EST) to clear the fault codes and verify that the BC2ECU1 message is actively being received.