Case IH 19855 – Engine Control Unit (ECU): Plausibility failure for turbine upstream temperature sensor.

This code indicates that the temperature reading coming from the Exhaust Gas Temperature (EGT) sensor located just before the turbocharger (turbine upstream) is illogical or "implausible". The control module compares this sensor's reading against other temperature sensors (such as coolant temperature, intake air temperature, or downstream exhaust temperature). If the engine has been sitting overnight (cold soak) but the upstream turbine sensor reads significantly hotter or colder than ambient/coolant temperatures, or if the temperature does not rise as expected under engine load, the system flags it as a plausibility failure.

• Tier 4b
• T7 Series
• Maxxum
• Puma
• Steiger
• N Series Loaders
• SR175 skid steers

1. 1

   Perform a cold soak comparison using the CNH Electronic Service Tool (EST) or a compatible scan tool to check live data for all temperature sensors after the machine has been sitting overnight; turbine upstream temperature should closely match coolant, intake air, and ambient temperatures.

2. 2

   Visually inspect the wiring harness and connector leading to the turbine upstream temperature sensor for melted wires, chafing, corrosion, or loose pins.

3. 3

   Inspect the exhaust manifold and the piping just before the turbocharger for soot trails or leaks, which can cause abnormal temperature readings.

4. 4

   Disconnect the sensor and measure its resistance with a multimeter, comparing the reading against the FPT engine specification chart for the ambient temperature to check for an open circuit or dead short.

1. 1

   Preparation

   Park the machine on a level surface, turn off the engine, and remove the key. Crucial: Allow the exhaust system and turbocharger to cool completely to prevent severe burns.

2. 2

   Locate the Sensor

   Locate the turbine upstream temperature sensor. It is threaded directly into the exhaust manifold or the exhaust piping immediately before the turbocharger inlet.

3. 3

   Disconnect Wiring

   Carefully unplug the electrical connector for the sensor. Move the harness aside so it does not get damaged during removal.

4. 4

   Remove the Sensor

   Spray the base of the sensor with penetrating oil and allow it to soak, as exhaust sensors frequently seize due to extreme heat cycles. Use a specialized EGT sensor socket or a flare-nut wrench to carefully unthread the sensor.

5. 5

   Prepare the New Sensor

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied from the factory). Note: Do not get any anti-seize on the sensor probe tip, as this will contaminate it and cause immediate failure.

6. 6

   Install the New Sensor

   Thread the new sensor in by hand to ensure it does not cross-thread, then tighten it to the OEM torque specification for your specific FPT engine model.

7. 7

   Reconnect

   Plug the electrical connector back in and ensure the locking tab clicks into place. Secure the wiring harness away from direct contact with the hot exhaust housing.

8. 8

   Clear Codes

   Turn the key ON, connect your diagnostic scan tool, and clear fault code 19855. Start the engine and monitor the live data to ensure the temperature rises smoothly and plausibly as the exhaust heats up.