Case IH 19767 – DCU: Catalyst temp. downstream sensor plaus. Error: Static Plausibility

The downstream temperature sensor on the Selective Catalytic Reduction (SCR) muffler is providing a reading that the system determines is not plausible, typically meaning the sensor's reading is stuck at a specific value and is not changing as expected when the exhaust heats up.

• Tier 4b
• Magnum 225
• Magnum 235-340
• Steiger 470
• Steiger 620
• Quadtrac 470
• Quadtrac 620
• Puma 160
• Puma 185
• Farmall 110A
• Farmall 120A
• Farmall 130A
• Farmall 140A
• AFX 6130
• AF 8250

1. 1

   Check for other active codes related to the upstream temperature sensor, NOx sensors, or base engine issues (EGR, Turbo, Fuel System) and correct them first.

2. 2

   Use an Electronic Service Tool (EST) to monitor upstream and downstream exhaust temperature sensors simultaneously; verify if the downstream sensor is stuck at a static value.

3. 3

   Inspect the wiring harness and connectors for the downstream temperature sensor for cracked insulation, heat damage, or corrosion.

4. 4

   Use a borescope camera to inspect the SCR honeycomb for crystallization or blockage, which can cause abnormal temperature differentials.

5. 5

   Ensure the ECU and Denoxtronic (DNox) unit have the latest software updates installed to prevent false plausibility faults.

1. 1

   Cool Down

   Turn off the engine and allow the exhaust and SCR system to cool completely to avoid severe burns.

2. 2

   Power Down

   Disconnect the battery or turn off the master disconnect switch.

3. 3

   Locate the Sensor

   Locate the downstream temperature sensor. It is positioned on the SCR muffler/catalyst exhaust outlet pipe, after the catalyst and NOx sensor.

4. 4

   Remove Heat Shields

   On some models (like the Farmall 130A), remove the SCR muffler and catalyst upper heat shield to access the sensor.

5. 5

   Disconnect and Remove

   Disconnect the electrical connector for the downstream temperature sensor. Carefully unthread the sensor from the exhaust pipe (penetrating oil may be required if the threads are seized).

6. 6

   Install New Sensor

   Thread the new OEM downstream temperature sensor into the exhaust outlet pipe and tighten to the manufacturer's specified torque. Reconnect the electrical connector.

7. 7

   Reassemble

   Reinstall any heat shields or clamps that were removed during access.

8. 8

   System Reset and Test

   Connect the EST laptop to clear the fault codes and reset the SCR system. Perform a test run under load to ensure the exhaust temperature reaches the 220–240 °C (428–464 °F) threshold required for DEF dosing to begin, and verify the new sensor reads dynamically.