Case IH 19177 – Engine ECU or NH3/NOx Sensor Control Box: NH3 sensor temperature invalid (too low or too high)

This code indicates that the internal temperature reading of the Ammonia (NH3) sensor in the exhaust aftertreatment system is registering outside of its expected operating range. When the sensor's internal heater fails or the temperature circuit malfunctions, it cannot accurately read ammonia levels, triggering this fault.

• Tier 4b
• Farmall (110U, 120U)
• Maxxum (115, 125, 135, 145, 150)
• Puma (140, 150, 165, 175, 185, 200, 220, 240)
• Optum (250, 270, 300)
• Luxxum series
• Farmlift series (e.g., 635)

1. 1

   Inspect the NH3 sensor probe in the exhaust pipe and its wiring harness for physical damage, melting, or chafing.

2. 2

   Disconnect the NH3 sensor control box connector and check for water intrusion, corrosion, or pushed-back pins.

3. 3

   Verify that the NH3 sensor control module is receiving proper battery voltage and has a solid ground connection.

4. 4

   Remove the sensor and check the probe for heavy soot packing or crystallized DEF (AdBlue) buildup, which can insulate the sensor and cause invalid temperature readings.

1. 1

   Preparation

   Turn off the engine, remove the key, and disconnect the battery to prevent electrical shorts. Allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the NH3 sensor on the exhaust aftertreatment system, typically mounted downstream of the SCR catalyst.

3. 3

   Disconnect

   Unplug the wiring harness from the NH3 sensor's electronic control unit/box.

4. 4

   Removal

   Carefully unscrew the NH3 sensor probe from the exhaust pipe bung. (Penetrating oil may be required if the threads are seized).

5. 5

   Installation

   Apply a small amount of anti-seize to the threads of the new sensor (avoiding the sensor tip) and thread it into the exhaust pipe. Tighten to the manufacturer's specified torque.

6. 6

   Reconnection

   Mount the new sensor's control box and plug the main wiring harness back into the module.

7. 7

   Clear Codes

   Reconnect the battery. Connect the Case IH Electronic Service Tool (EST) to the machine's diagnostic port to clear fault code 19177 and perform any required aftertreatment resets or sensor initialization procedures.