Case IH 19012 – DCU (Dosing Control Unit) or Engine ECU: NH3 sensor open in heater circuit causing under-heating.

The NH3 (ammonia) sensor is a critical component of the Tier 4 Selective Catalytic Reduction (SCR) emissions system. It is located mid-bed on the SCR catalyst and detects the ammonia concentration in the exhaust to ensure the catalyst is reducing NOx properly. The sensor relies on an internal heater to reach operating temperature. An "open in heater circuit" indicates a break in the electrical path (either in the wiring or the sensor's internal heating element), preventing the sensor from heating up, which triggers an SCR system failure and potential engine derate.

• Tier 4b
• 240 Series Axial-Flow Combines
• Patriot Sprayers
• Steiger
• Magnum
• Puma
• Maxxum
• 580N Backhoes

1. 1

   Visually inspect the wiring harness and connectors leading to the NH3 sensor on the SCR catalyst for melted wires, corrosion, or disconnected pins.

2. 2

   Isolate the components by disconnecting the slide-lock connector that separates the NH3 sensor probe from the NH3 sensor module.

3. 3

   Using a digital multimeter, measure the trim resistance of the NH3 sensor probe heater circuit at the connector pins (must be between 500 and 2000 ohms). An open circuit indicates internal failure.

4. 4

   Check for manufacturer updates (TSB 150105) to verify if the machine is eligible for the CNH/Cummins SCR update campaign, which obsoletes the 3-bung SCR catalyst in favor of a 2-bung catalyst and deletes the NH3 sensor.

1. 1

   Safety Prep

   Turn off the engine and disconnect the batteries (negative cable first) to prevent arcing.

2. 2

   Cool Down

   Wait for the exhaust and aftertreatment SCR system to completely cool down. The SCR catalyst retains extreme heat for long periods after shutdown.

3. 3

   Disconnect Sensor

   Locate the NH3 sensor on the SCR catalyst. Disconnect the slide-lock electrical connector that joins the NH3 sensor probe to the NH3 sensor module.

4. 4

   Remove Probe

   Carefully unscrew the faulty NH3 sensor probe from the SCR catalyst bung.

5. 5

   Install New Part

   Install the new NH3 sensor probe into the exhaust bung and tighten to OEM torque specifications. Reconnect the slide-lock connector to the module. (Replace the module instead only if diagnostic testing proved the module was at fault rather than the probe).

6. 6

   Reassemble and Clear

   Reconnect the battery cables. Use the Case IH Electronic Service Tool (EST) or a compatible diagnostic scanner to clear the 19012 fault code. Run the machine to operating temperature or perform a manual SCR system test to verify the code does not return.