Case IH 19775 – DCU (Dosing Control Unit) / DCU15: Group error path catalyst temperature _Error belonging to group catalyst temperature out of range _P0426 Plausibility of catalyst temperature sensors - Plausibility error (static)

The engine control unit has detected that the ratio between the downstream exhaust temperature sensor and the upstream temperature sensor is below the acceptable threshold or reading implausible data.

• Tier 4a
• Case IH Magnum Series: 180, 200, 220, 235, 240, 250, 280, 310, 340, 380
• Case IH Steiger 4WD Tractors: 350, 370, 400, 420, 450, 470, 500, 550, 600
• Case IH Maxxum & Puma Series: 115 through 220
• Case IH Axial-Flow Combines: 7230, 8230, 9230

1. 1

   Check the urea tank for contaminated, diluted, or expired DEF/AdBlue (poor fluid quality is a leading cause of low NOx conversion efficiency)

2. 2

   Inspect the muffler and exhaust gas piping for physical damage or leaks that could skew sensor readings

3. 3

   Check the NOx sensor and catalyst temperature sensor wiring harnesses for damaged/loose machine earths, pushed-out connector pins, or water intrusion (often caused by pressure washing)

4. 4

   Verify that the upstream and downstream catalyst temperature sensors are installed correctly and reading accurately (specifically for Code 19775)

1. 1

   Power Down

   Turn off the ignition and disconnect the tractor's battery to prevent electrical shorts and reset the DCU.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor probe mounted in the exhaust pipe behind the SCR catalyst.

3. 3

   Disconnect Wiring

   Disconnect the NOx sensor module's 5-pin electrical connector (MCON plug). Detach the wiring harness from any retaining clips.

4. 4

   Remove the Sensor

   Use an appropriate sensor socket or wrench to remove the NOx sensor probe from the exhaust housing.

5. 5

   Install New Sensor

   Thread the new NOx sensor into the exhaust and tighten to OEM torque specifications.

6. 6

   Route the Harness Safely

   When routing the new harness, ensure no connectors are mounted vertically. Horizontal mounting or connecting from below is required to provide a "drip loop" that prevents water intrusion. Secure with clips to avoid abrasion.

7. 7

   Clear Codes and Relearn

   Reconnect the battery. Use an Electronic Service Tool (EST) or OBD2 scanner to clear the DCU error codes.

8. 8

   Validation Drive

   The code may remain in a "pending" state until the SCR system verifies the repair. Bring the engine to operating temperature and run it under load for up to 30 minutes until the system registers that NOx efficiency is back within the threshold.