Case IH 19050 (DTC 478E) - ECU – Engine Control Unit (ECU) / Engine Management System (EMS): Downstream NOx sensor supply voltage is out of range.

The Engine Management System has detected that the electrical supply voltage going to the downstream Nitrogen Oxide (NOx) sensor is outside of the expected operating parameters. The downstream NOx sensor is located directly after the Selective Catalytic Reduction (SCR) catalyst and measures the pollutants exiting the tailpipe to monitor the efficiency of the emissions system. When this code is triggered, the machine will typically log an SCR failure, illuminate a warning light, and eventually initiate an engine power loss/derate to protect the system.

• MAXXUM T4E
• Case IH 240 Series Axial-Flow Combines
• Case IH Magnum Tractors (e.g., 250-380 series)
• Case IH Steiger Tractors
• Case IH Farmall Tractors (Tier 4B / Stage V with Cab and CVT)
• Case Construction wheel loaders (e.g., 1021G)

1. 1

   Check the downstream NOx sensor wiring harness and connectors for physical damage, corrosion, or loose pins

2. 2

   Verify that the alternator output voltage is within specification, as a defective alternator can cause voltage spikes or drops

3. 3

   If the machine is equipped with a dedicated voltage converter for the emissions sensors, test it for proper output

4. 4

   Ensure the sensor is assembled correctly and verify that no aftermarket tuning chips are installed, as these can interfere with the NOx sensor signal and trigger false voltage codes

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical shorts during repair.

2. 2

   Harness Repair (If Applicable)

   If the diagnostic checks revealed a short or open circuit in the wiring harness between the ECU and the sensor, repair or replace the damaged wiring section.

3. 3

   Sensor Replacement

   If the wiring and supply voltage from the ECU/alternator are confirmed good, the downstream NOx sensor itself has failed internally. Locate the sensor on the exhaust pipe directly downstream of the SCR catalyst.

4. 4

   Removal

   Disconnect the sensor's electrical connector and use a specialized NOx/O2 sensor socket to carefully unthread the sensor from the exhaust pipe.

5. 5

   Installation

   Apply a small amount of anti-seize to the threads of the new sensor (if not pre-applied from the factory) and thread it into the exhaust pipe. Torque to the manufacturer's specification. Reconnect the electrical harness.

6. 6

   System Reset

   Reconnect the battery. Use a diagnostic scan tool to clear the 19050 (478E) fault code.

7. 7

   Validation Restart

   Perform an SCR system validation restart. Ensure the DEF/AdBlue tank level is raised above 12% total volume. Follow the specific key cycle and engine run sequence for your model to clear the engine power derate and allow the ECU to recognize the new sensor.