Case IH tB2 – Central Controller (XCM) / Engine Control Module (ECM): Vehicle CAN Bus Off, Data Valid But Above Normal Range

This code indicates a communication failure on the Controller Area Network (CAN) bus. Specifically, it points to a faulty connection or loss of communication between the Central Controller (XCM) and the Engine Control Module (ECM/EDC). The system is receiving a valid data signal, but the value is above the normal operating threshold, forcing the CAN bus to shut off to protect the network. The engine remains enabled with no restriction on fuel or speed, but hand throttle functions may be disabled.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190

1. 1

   Check for Active Interference: Verify there is no external electromagnetic interference disrupting the CAN BUS network.

2. 2

   Inspect Connectors: Check the main harness connectors at both the XCM (located in the panel behind the operator's seat or under the EDC panel) and the ECM. Look for pushed-back pins, corrosion, or moisture.

3. 3

   Verify CAN Bus Resistance: With the tractor off and the battery disconnected, measure the resistance across the CAN High and CAN Low pins. A healthy CAN bus should read approximately 60 ohms. A reading of 120 ohms indicates an open circuit or a missing terminating resistor.

4. 4

   Check for Related Codes: Look for accompanying codes like tB3 (Vehicle CAN Bus Off, Shorted To High Source) which can help pinpoint a dead short in the harness.

1. 1

   Power Down

   Turn off the tractor ignition and disconnect the negative battery cable to prevent electrical damage during testing.

2. 2

   Locate Modules

   Locate the Central Controller (XCM) behind the operator's seat/EDC panel and the Engine Control Module (ECM).

3. 3

   Harness Inspection

   Trace the CAN bus wiring harness between the XCM and the ECM. Inspect the physical condition of the wires for chafing, rodent damage, or melted insulation.

4. 4

   Continuity Testing

   Disconnect the harness at both modules. Using a multimeter, perform a continuity test on the CAN High and CAN Low wires from end to end. The resistance should be less than 1 ohm. If the resistance is high (or shows an open circuit/OL), the harness is broken.

5. 5

   Short-to-Ground/Power Test

   Test the CAN wires for continuity to ground (tractor chassis) and to the 12V power supply wire. Any continuity here indicates a short circuit.

6. 6

   Repair or Replace

   If a broken or shorted wire is found, either repair the specific wire using OEM-approved splicing methods or replace the affected CAN-Bus wiring harness section.

7. 7

   Clean and Reconnect

   Clean all module pins with electronic contact cleaner. Reconnect the harness to the XCM and ECM securely.

8. 8

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use the tractor's H-Menu or a diagnostic service tool to clear the stored 3650/tB2 fault code. Start the engine to verify the code does not return and that hand throttle functions are restored.