Case IH 19021 – DCU (Dosing Control Unit / DeNOx Module): Temperature sensor before catalyst (electrical) – signal high – signal above high error threshold

The control module is receiving a voltage signal from the upstream exhaust catalyst temperature sensor that exceeds the maximum allowable limit. A "signal high" condition typically points to an open circuit, a broken wire, a short to a power source, or an internally failed sensor.

• Tier 4a
• Magnum series (235–340 Series 4)
• Puma series (125, 140, 210)
• Steiger series
• Farmall series
• 580N EP Backhoe Loaders
• 621F Wheel Loaders
• 721F Wheel Loaders
• 821F Wheel Loaders
• 921F Wheel Loaders

1. 1

   Perform a plausibility check using a diagnostic tester to read live data for the temperature sensor before catalyst. If the engine is cold, the reading should roughly match ambient temperature; a maxed out or implausible reading confirms a failure.

2. 2

   Inspect the wiring harness and connectors between the temperature sensor and the DCU. Look for broken wiring inside the UREA pump module harness, corrosion at the pins, or melted insulation causing a short to power.

3. 3

   Disconnect the sensor and perform a continuity test on the harness to check for proper voltage and isolate whether the open/short is in the wiring harness or the sensor itself.

1. 1

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical spikes.

2. 2

   Locate the "before catalyst" temperature sensor on the exhaust system (upstream of the DOC/SCR catalyst assembly).

3. 3

   Disconnect the sensor's electrical connector. Check the connector pins for dirt, moisture, or corrosion. Clean if necessary.

4. 4

   If the diagnostic checks proved the wiring harness is intact and the fault is isolated to the sensor, remove the faulty temperature sensor from the exhaust pipe.

5. 5

   Install the new replacement temperature sensor and torque to OEM specifications.

6. 6

   Reconnect the wiring harness, ensuring the connector is fully seated and locked to prevent moisture intrusion.

7. 7

   Reconnect the battery, turn on the machine, and use a diagnostic tool to clear the inactive 19021 fault code.

8. 8

   Run the engine and verify via live data that the sensor is now reading the exhaust temperature accurately.

   Note: OEM documentation states that if the error is still present after replacing the sensor and verifying the wiring, the DCU/Pump Module itself may require replacement, though this is rare.