Case IH 19770 – Engine Control Unit (ECU) / Engine Control Module (ECM): SCR catalyst upstream temperature sensor static plausibility

The engine control system has detected that the temperature reading from the Selective Catalytic Reduction (SCR) upstream temperature sensor is "static" or implausible. This means the sensor's reported temperature is stuck at a specific value and is not fluctuating as expected when the exhaust system heats up or cools down during normal engine operation.

• Tier 4b
• Maxxum
• Farmall
• Magnum
• Steiger
• Quadtrac
• Axial-Flow (AF / AFX) series
• 8250

1. 1

   Inspect the wiring harness leading to the SCR upstream temperature sensor for chafing, melting, or breaks.

2. 2

   Disconnect the sensor and check the 2-cavity connector and terminal pins for oxidation, corrosion, or pushed-out pins.

3. 3

   Perform a cold soak comparison using the Case IH Electronic Service Tool (EST): the SCR upstream temperature sensor should read roughly the same as ambient air, DOC upstream, and SCR downstream sensors.

4. 4

   Perform dynamic testing: start the engine and monitor the sensor via EST. Temperature should steadily rise to 300-330 °C (572-626 °F) under load. A static value indicates an internally shorted or stuck sensor.

5. 5

   Perform a disconnect test: disconnect the sensor while monitoring EST. If the code changes to voltage too high/low, the wiring to the ECU is intact, confirming a failed sensor.

1. 1

   Preparation

   Ensure the machine is parked on a level surface, the engine is turned off, and the exhaust system has completely cooled to prevent severe burns. Disconnect the battery ground.

2. 2

   Locate the Sensor

   Locate the SCR upstream temperature sensor. It is threaded into the exhaust pipe directly before the SCR catalyst / dosing module.

3. 3

   Disconnect Wiring

   Unplug the sensor's electrical connector from the main engine wiring harness.

4. 4

   Remove the Sensor

   Carefully unscrew the temperature sensor from the exhaust pipe bung. Note: Exhaust sensors can seize due to high heat cycles; penetrating oil may be required.

5. 5

   Install the New Sensor

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied from the factory) and thread it into the exhaust pipe. Tighten to the OEM torque specification.

6. 6

   Reconnect

   Plug the sensor's electrical connector back into the harness, ensuring the locking tab clicks into place.

7. 7

   Clear and Verify

   Reconnect the battery. Connect the EST, clear the 19770 fault code, and run the engine under load to verify that the temperature reading now fluctuates correctly and the code does not return.