Case IH 3097 – Engine Control Module (ECM) / Engine ECU: ECM Bus Off on Engine private CAN

The Engine Control Module (ECM) has detected a critical communication failure on its private Controller Area Network (CAN) bus. It has experienced too many transmission errors and intentionally disconnected itself to prevent corrupting the rest of the network.

• Case IH Magnum Series 235, 260, 290, 315, 340 (Series 4)
• Case IH Steiger Series
• Case IH Optum Series
• Case IH Puma Series
• Case IH Maxxum Series

1. 1

   Visual Harness Inspection: Check the engine wiring harness for physical damage, rubbing, or pinched wires, particularly where the harness routes near the engine block, exhaust components, or cab pivot points.

2. 2

   Terminating Resistor Check: With the machine powered off and the battery disconnected, measure the resistance between the CAN High and CAN Low pins on the private CAN diagnostic port or connector. A healthy CAN bus should read approximately 60 ohms. If the reading is 120 ohms, one terminating resistor is missing, faulty, or there is an open circuit in the wiring. If the reading is Open (OL), both resistors are missing, or there is a complete break in the main bus wiring.

3. 3

   Short Circuit Checks: Measure the resistance from CAN High to Ground, CAN Low to Ground, and CAN High to CAN Low to ensure the wires are not shorted to each other or to the chassis.

4. 4

   Connector Inspection: Inspect the connectors at the ECM and the Dosing Control Unit (DCU) for pushed-out pins, corrosion, or water ingress.

1. 1

   Disconnect Power

   Disconnect the battery to prevent electrical damage during the repair.

2. 2

   Isolate the Fault

   Based on the resistance checks, locate the break or short in the private CAN harness. If the resistance was 120 ohms, locate the external terminating resistor on the harness (note: the ECM usually contains one internal resistor, while the other is external or located in another module like the DCU).

3. 3

   Repair the Wiring

   If a wire is broken or chafed, cut out the damaged section. Using an approved CNH electrical harness repair kit, splice in new wiring. Crucial: You must maintain the twist rate of the CAN wires (typically one twist per inch) to ensure the network remains shielded from electromagnetic interference.

4. 4

   Replace Terminating Resistor

   If the wiring is intact but the external terminating resistor tests open or out of spec, cut the resistor connector out and splice in a replacement, or plug in a new resistor if it is a modular plug-in type.

5. 5

   Reassemble and Clear Codes

   Reconnect all modules and the battery. Connect the Case IH Electronic Service Tool (EST) to the diagnostic port, clear the inactive 3097 fault code, and cycle the key to verify the ECM successfully communicates on the private CAN without going 'Bus Off'.