Case IH 12700 – Engine Control Unit (ECU / ECM) or central CAN gateway: CAN communication error on CAN C circuit

CAN data is missing due to a voltage anomaly on the CAN C circuit. The system detects that the CAN High (CAN Hi) and CAN Low (CAN Lo) voltages are either not present, or the CAN Hi voltage is not at least 0.1V greater than the CAN Lo voltage, resulting in a loss of data transmission between modules.

• Magnum
• Steiger
• Puma
• combines

1. 1

   Locate the inline CAN connectors (specifically checking pins 2 and 6 depending on the harness).

2. 2

   Turn the key switch on and measure the voltage on the CAN circuit: CAN Hi should have between 2.0V and 4.0V.

3. 3

   Verify that both CAN Lo and CAN Hi have voltage present, and ensure that CAN Hi is at least 0.1V greater than CAN Lo.

4. 4

   Turn the key switch off and check the CAN C circuit resistance. A healthy CAN bus should read approximately 60 ohms (indicating two 120-ohm terminating resistors are intact).

5. 5

   Refer to the specific vehicle service manual and electrical schematics to trace the CAN C circuit if voltages are out of spec.

1. 1

   Power down the machine and disconnect the battery to prevent electrical shorts during testing.

2. 2

   Locate the CAN diagnostic connectors or inline connectors for the affected circuit.

3. 3

   Perform the voltage and resistance checks mentioned in the diagnostic steps.

4. 4

   If the voltage is missing or CAN Hi is not >0.1V above CAN Lo, visually inspect the wiring harness for chafing, breaks, shorts to ground, or severe corrosion at the connectors.

5. 5

   Inspect the CAN terminating resistors. If the resistance check yields 120 ohms, one resistor is faulty or there is an open circuit in the harness. If it yields 0 ohms, there is a short.

6. 6

   Repair or replace the damaged wiring harness section, corroded connector pins, or faulty CAN terminating resistor.

7. 7

   Reconnect the battery, turn the key on, and clear the fault code using the Case IH Electronic Service Tool (EST).