Case IH F-172-02 - ECU – Engine Control Unit (ECU): Plausibility check error of the humidity sensor air temperature sensor at cold start only.

This is a logic/plausibility error. When the machine undergoes a 'cold soak' (sitting turned off long enough for the engine to cool to ambient temperature), the control module compares the temperature reading from the intake air humidity/temperature sensor against other engine temperature sensors (such as the coolant temperature, oil temperature, and intake manifold temperature). If the air temperature reading from the humidity sensor deviates significantly from the other sensors, the module flags the reading as 'implausible' and triggers this code.

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• Case IH Farmall Series (40, 45, 50)
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• Case IH / New Holland T7 Series (Tier 4B)

1. 1

   Perform a cold soak verification by letting the machine sit overnight (at least 8 hours) so all engine components equalize to ambient temperature.

2. 2

   Connect a diagnostic scan tool before starting the engine and compare live data for all temperature sensors (Humidity Sensor Air Temperature, Intake Manifold Air Temperature, Engine Coolant Temperature, and Engine Oil Temperature). If the humidity/air temperature sensor is the only outlier, the sensor is likely faulty.

3. 3

   Inspect the wiring harness and the electrical connector at the humidity sensor for moisture intrusion, corrosion on the pins, or chafed wires.

4. 4

   Check for accompanying CAN communication fault codes (such as SPN 3519 - CAN Signal Failure for Humidity Sensor) which would indicate a wiring or network issue rather than a failed sensor element.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Locate the Sensor

   Locate the humidity/air temperature sensor. On FPT engines, it is mounted on the engine air suction/intake pipe, downstream of the main air filter housing.

3. 3

   Disconnect

   Carefully depress the locking tab and disconnect the electrical connector from the sensor.

4. 4

   Remove

   Unscrew or unclip the faulty sensor from the intake pipe.

5. 5

   Install

   Insert the new OEM humidity/air temperature sensor into the intake pipe. If it is a threaded sensor, torque it to the manufacturer's specification (do not overtighten, as the intake piping is often plastic).

6. 6

   Reconnect

   Plug the electrical connector back into the sensor, ensuring the weather-seal is intact and the lock clicks into place.

7. 7

   Clear Codes

   Reconnect the battery, turn the ignition on, and use a diagnostic scan tool to clear the F-172-02 / 19197 fault code.

8. 8

   Test

   Perform a cold start to verify the repair and ensure the ECU no longer detects a plausibility mismatch.