Case IH 19020 (DTC 2B1A) - ECU – DCU (Dosing Control Unit): Upstream SCR catalyst temperature sensor voltage is lower than expected

Indicates a short circuit to ground in the sensor wiring or a complete internal failure of the sensor itself. The standard OBD-II equivalent for this code is P0427.

• MAXXUM T4E
• 240 Series Axial-Flow Combines
• Magnum 235–340 (Series 4)
• Steiger 350–600
• Farmall CVT tractors

1. 1

   Perform a plausibility check using a diagnostic tester on a completely cold engine to ensure the 'Temperature sensor before catalyst' reading matches the ambient outside temperature.

2. 2

   Inspect the wiring harness and connectors between the upstream SCR temperature sensor and the DCU, specifically looking for a short circuit to ground or broken wiring.

3. 3

   Disconnect the sensor to see if the fault state changes (e.g., from a 'low' circuit code to a 'high' or 'open' circuit code). If the code changes, the wiring is likely intact, and the sensor is the culprit.

1. 1

   Power Down

   Turn off the machine and turn off the battery disconnect switch. Ensure the exhaust system has completely cooled down to avoid severe burns.

2. 2

   Locate the Sensor

   Locate the Diesel Oxidation Catalyst (DOC) and SCR catalyst assembly on the exhaust system. Identify the upstream temperature sensor (the sensor located before the SCR catalyst chamber).

3. 3

   Inspect and Clean

   Inspect the sensor connector for water intrusion, melted pins, or corrosion. Clean if necessary.

4. 4

   Replace the Sensor

   If the wiring harness tested good during diagnostics, unscrew the faulty upstream SCR temperature sensor from the exhaust bung.

5. 5

   Install the New Sensor

   Apply a high-temperature anti-seize compound to the threads of the new sensor (if not pre-applied) and torque it to the manufacturer's specification. Reconnect the electrical harness.

6. 6

   Clear Codes

   Reconnect the battery, turn the key on, and use a diagnostic tool to clear the 19020 / 2B1A fault code.

7. 7

   Verify Repair

   Start the engine and monitor the upstream SCR temperature via the diagnostic tool to ensure it rises smoothly as the exhaust heats up.