Case IH 3700 (DTC 3754) - ECU – Engine Control Unit (ECU): Intake air humidity sensor value is not plausible.

The system is performing a plausibility check on the humidity sensor signal, and the data being reported back to the computer does not align with expected operational parameters (it is reading a value that is logically impossible or out of the expected range for the current environment).

• MAXXUM T4E
• 240 Series Axial-Flow Combines
• 5130
• Magnum 250-380 series
• Puma series
• Puma 240
• Farmall series
• WD1505

1. 1

   Inspect the sensor element for physical water droplets (moisture)

2. 2

   Inspect the wiring harness for a short circuit to ground (SRC low)

3. 3

   Inspect the wiring for a short circuit to an external voltage source (SRC high)

4. 4

   Check for a disturbed CAN signal transmission or a sensor message problem

5. 5

   Verify if the signal value is pegged above the maximum limit, which usually indicates a dead or defective sensor

1. 1

   Locate the Sensor

   Find the intake air humidity sensor in the inlet air plumbing between the air filter and the turbocharger.

2. 2

   Inspect the Connection

   Disconnect the sensor's electrical connector. Inspect the pins for corrosion, bent terminals, or moisture intrusion.

3. 3

   Clear Moisture

   Remove the sensor and inspect the probe. If water droplets are present in the intake tract or on the sensor, carefully dry the sensor and the plumbing. Reinstall and test to see if the code clears.

4. 4

   Test the Harness

   Using a multimeter, verify continuity in the wiring harness back to the ECU. Ensure there are no shorts to ground or shorts to voltage in the signal wires.

5. 5

   Replace the Sensor

   If the wiring harness tests good, the connector is clean, and the sensor is dry but the 3700 (DTC 3754) code remains active, the sensor itself has failed internally and must be replaced.

6. 6

   Clear Codes

   After replacement, use a diagnostic tool to clear the ECU fault codes and run the engine to ensure the DEF/AdBlue dosing system returns to normal operation.