Case IH F-4377-09 - ECU – Engine Control Unit (ECU) or Aftertreatment Control Module (ACM): CAN timeout error from NH3 sensor - NH3Sens message

The control module is not receiving the expected data messages from the Ammonia (NH3) sensor over the CAN (Controller Area Network) bus within the required timeframe.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Farmall series (110U)
• Maxxum series (115)
• Magnum
• Steiger

1. 1

   Check for multiple codes: Verify if other CAN bus devices are also logging timeout errors. If multiple sensors are offline, the issue is likely a main CAN bus wiring failure or ECU issue, not the NH3 sensor itself.

2. 2

   Inspect the wiring harness between the NH3 sensor and the ECU/ACM for chafed wires, melted insulation near the exhaust, or moisture intrusion.

3. 3

   Disconnect the NH3 sensor and check the connector pins for corrosion, pushed-back terminals, or loose connections.

4. 4

   Verify that the sensor is receiving proper operating voltage and has a solid ground.

5. 5

   Measure CAN bus resistance: With the batteries disconnected, measure the resistance across the CAN High and CAN Low pins at the sensor connector. A healthy CAN bus should read approximately 60 ohms.

1. 1

   Disconnect battery

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical spikes.

2. 2

   Locate sensor

   Locate the NH3 sensor on the exhaust aftertreatment (SCR) pipe (typically downstream of the SCR catalyst).

3. 3

   Disconnect connector

   Disconnect the electrical connector from the NH3 sensor module.

4. 4

   Remove sensor

   Carefully unscrew the NH3 sensor from the exhaust bung. (Penetrating oil may be required if the sensor is seized from exhaust heat).

5. 5

   Apply anti-seize

   Apply a high-temperature anti-seize compound to the threads of the new NH3 sensor (if not already pre-applied by the manufacturer). Ensure no compound gets on the sensor tip.

6. 6

   Install new sensor

   Install the new NH3 sensor into the exhaust pipe and tighten to the OEM torque specification.

7. 7

   Reconnect harness

   Reconnect the electrical harness, ensuring the locking tab clicks into place.

8. 8

   Reconnect battery

   Reconnect the battery.

9. 9

   Clear fault code

   Connect a diagnostic service tool (such as the Case IH EST) to clear the F-4377-09 fault code.

10. 10

    Verify repair

    Start the engine and allow it to reach operating temperature to verify the CAN communication is restored and the code does not return.