Case IH 19014 – Engine Control Unit (ECU) / Engine Control Module (ECM): NH3 sensor open or short in trim resistor circuit

The engine's control system has detected an electrical fault—either an open circuit (disconnected/broken wire) or a short circuit—specifically on the trim resistor line of the Aftertreatment Intermediate NH3 (Ammonia) Sensor. This sensor monitors the exhaust stream to ensure the Selective Catalytic Reduction (SCR) system is properly dosing DEF/AdBlue to reduce emissions.

• Tier 4b
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Maxxum
• Magnum
• Steiger
• Patriot Sprayers (2240, 3230, 3330)

1. 1

   Inspect the NH3 sensor wiring harness and the sensor shroud connector for physical damage, melted wires, or severe corrosion.

2. 2

   Verify the trim resistor pins and wiring (Yellow wire for trim resistor, Tan wire for trim resistor ground).

3. 3

   Use a multimeter to check for continuity on the trim resistor signal and return lines back to the ECU, and test for a short to ground or short to voltage.

4. 4

   Verify that the ECU is supplying the correct 5-volt reference to the sensor supply circuit.

1. 1

   Power Down

   Turn off the machine and turn off the battery disconnect switch to prevent electrical spikes.

2. 2

   Harness Repair

   If the diagnostic checks reveal a broken wire or chafed insulation on the trim resistor circuit between the ECU and the sensor, repair the wiring harness using OEM-approved waterproof splices or replace the affected harness section.

3. 3

   Sensor Replacement

   If the harness tests perfectly, the fault lies within the NH3 sensor's internal trim resistor. Disconnect the electrical connector from the NH3 sensor located in the exhaust aftertreatment plumbing. Carefully unthread the faulty NH3 sensor from the exhaust pipe. Apply high-temperature anti-seize to the threads of the new sensor (if not pre-applied) and install it into the exhaust plumbing. Reconnect the electrical harness.

4. 4

   Clear Codes

   Restore battery power, connect a diagnostic tool (such as the Case IH Electronic Service Tool), and clear the inactive 19014 fault code.

5. 5

   Validation

   Run the engine to operating temperature so the SCR system engages and verify that the fault code does not return and no engine power loss/derate occurs.