Case IH 19017 (DTC 38EE) – Engine Control Unit (ECU): NH3 sensor signal out of range failure

The NH3 (Ammonia) sensor measures the amount of ammonia within the exhaust flow after the Selective Catalytic Reduction (SCR) catalytic reaction. This code triggers when the data reported by the sensor falls outside the expected normal operating parameters.

• MAXXUM T4E
• Case IH 240 Series Axial-Flow Combines (e.g., 7240, 8240, 9240)
• Case IH Magnum Tractors (e.g., 180, 200, 220, 240, 250-380)
• Case IH Farmall and Maxxum Tractors (Tier 4B models)

1. 1

   Check for related codes, such as DTC EBDE (19014) 'NH3 sensor open or short in trim resistor circuit,' which would point to a hard electrical failure rather than a sensor reading issue.

2. 2

   Inspect the wiring harness connecting the NH3 sensor processor to the Engine ECU. Look for chafed wires, corrosion, or loose pins on the CAN data bus lines.

3. 3

   Ensure there are no exhaust leaks around the Diesel Oxidation Catalyst (DOC) or SCR muffler that could skew the sensor's readings.

4. 4

   Verify that the Diesel Exhaust Fluid (DEF) is uncontaminated, as poor DEF quality can cause abnormal ammonia slip after the SCR catalyst, pushing the sensor readings out of range.

1. 1

   Cool Down

   Turn off the engine and allow the exhaust system (specifically the SCR muffler and clean-up catalyst area) to cool completely, as the sensor operates in a high-temperature environment.

2. 2

   Disconnect

   Locate the NH3 sensor assembly downstream of the SCR catalyst. Disconnect the electrical harness from the NH3 sensor's processor module.

3. 3

   Removal

   Carefully unthread the NH3 sensor probe from the exhaust pipe/muffler bung.

4. 4

   Installation

   Install the replacement NH3 sensor into the exhaust stream.

5. 5

   Reconnect

   Plug the machine's wiring harness back into the new sensor's processor module.

6. 6

   Clear and Test

   Use a diagnostic tool to clear the 19017 (38EE) fault code. Run the engine, allow the exhaust to reach operating temperature, and verify that the supply module builds pressure and the sensor reaches a 'Ready' state without the code returning.