Case IH 19016 – Dosing Control Unit (DCU) or Engine Control Unit (ECU): NH3 sensor heater performance failure

The NH3 (Ammonia) sensor is located in the exhaust aftertreatment system and monitors the Selective Catalytic Reduction (SCR) process. The sensor contains a built-in heating element designed to bring it up to operating temperature quickly and prevent condensation. A "performance failure" indicates that the heater circuit is not operating within expected parameters—likely drawing incorrect current or failing to reach the target temperature in the required timeframe.

• Tier 4b
• Magnum (235-340)
• Maxxum (115, 125, 135, 145, 150)
• Puma (140, 150, 165, 175, 185, 200, 220, 240)
• Optum (250, 270, 300)
• Farmall (110U, 120)
• Luxxum
• 240 Series Combines
• TR340 Compact Track Loaders
• 580N Backhoe Loaders

1. 1

   Disconnect the batteries and wait for the aftertreatment system to completely cool down before working on the exhaust.

2. 2

   Check the wiring harness and the slide-lock connector between the sensor probe and the module for melted wires, corrosion, or loose connections.

3. 3

   Disconnect the slide-lock connector and remove the NH3 sensor probe from the module. Using a digital multimeter, measure the trim resistance of the NH3 sensor probe. The trim resistance must measure between 500 and 2000 ohms. If it falls outside this range, the probe's heater has failed and the probe must be replaced.

1. 1

   Ensure the exhaust system is cool and the negative battery cable is disconnected.

   Safety precaution before beginning repair.

2. 2

   Locate the NH3 sensor in the exhaust system.

   Typically located after the SCR muffler or in the middle of the SCR catalyst.

3. 3

   Disconnect the electrical connector linking the sensor probe to the control module.

   Prepare for component removal.

4. 4

   If replacing the probe: Unscrew the probe from the exhaust pipe.

   Standard thread size is M18 x 1.5. Apply high-temperature anti-seize compound to the threads of the new probe (if not already pre-applied by the manufacturer). Install and tighten the new probe.

5. 5

   If replacing the module: Unbolt the module from the sensor table/bracket on the SCR catalyst and install the new unit.

   Replace the electronic control unit portion of the sensor assembly.

6. 6

   Reconnect the slide-lock electrical connectors and restore battery power.

   Restore electrical connections.

7. 7

   System Reset: Clear the fault codes using a diagnostic tool (such as the EASy tool).

   Note: If the machine was forced into a torque/RPM reduction mode (derate) due to this emissions fault, a "Startup counter reset" must be performed via the diagnostic tester to unlock the machine and return it to normal operation mode.