Case IH F-4383-31 - ECU – Engine ECU: NH3 sensor: Internal sensor heater control failure

The NH3 (Ammonia) sensor is a critical component of the Selective Catalytic Reduction (SCR) emissions system. To accurately measure ammonia slip in the exhaust gas, the sensor relies on an internal heating element to reach a specific operating temperature. This code triggers when the system detects an electrical fault, insufficient heating, or a power supply failure specifically related to the sensor's internal heater circuit.

• MAGNUM AFS Connect
• Farmall series (e.g., 90C, 110U, 130A)
• Maxxum series (e.g., 115)
• Steiger Rowtrac
• 240 Series Axial-Flow Combines
• 580N Backhoe Loaders

1. 1

   Visually inspect the wiring harness between the NH3 sensor and the NH3 sensor controller (the sensor's dedicated mini-ECU).

2. 2

   Check wiring integrity for chafed wires, melted insulation from exhaust heat, or disconnected plugs.

3. 3

   Disconnect the sensor and check the pins for corrosion, moisture, or pushed-out terminals.

4. 4

   Check for underlying CAN bus timeout errors or battery voltage issues, as a drop in voltage can sometimes trigger false heater supply failures.

5. 5

   If the visual inspection and wiring checks pass without issue, the internal heater is burned out and the sensor must be replaced.

1. 1

   Cool down exhaust

   Ensure the machine is turned off and the exhaust system has completely cooled, as the sensor is located directly on the SCR muffler/catalyst.

2. 2

   Locate the sensor

   Locate the NH3 sensor, which is mounted downstream of the SCR catalyst (often near the downstream temperature sensor).

3. 3

   Remove heat shields

   If applicable to your specific model, remove the SCR muffler/catalyst upper heat shields to gain access.

4. 4

   Disconnect wiring

   Unplug the wiring harness connecting the NH3 sensor's electronic control unit to the main engine harness.

5. 5

   Remove sensor

   Carefully unscrew the NH3 sensor from the exhaust pipe.

6. 6

   Install new sensor

   Thread the new NH3 sensor into the exhaust bung and tighten to OEM torque specifications.

7. 7

   Reconnect wiring

   Mount the attached sensor control unit and plug the connector back into the main harness.

8. 8

   Clear codes

   Use a diagnostic tool (such as the Case IH EST) to clear the F-4383-31 fault code and reset the emissions system.