Case IH F-354-01 - ECU – Engine Control Unit (ECU): Intake air humidity sensor voltage is lower than expected.

The signal voltage from the induction air humidity sensor has dropped below the minimum acceptable threshold. The underlying condition is typically a short circuit to ground in the sensor's wiring harness, a defective sensor, or water droplets accumulating inside the sensor.

• MAGNUM AFS Connect
• Case IH Magnum 250-380
• Steiger
• Puma
• Farmall series
• 240 Series Axial-Flow Combines (e.g., 5130)
• Case 621G
• Case 721G

1. 1

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

2. 2

   Visually inspect the sensor for moisture. A sensor full of water droplets can trigger this low-voltage fault.

3. 3

   Inspect the sensor's electrical connector and wiring harness for physical damage, chafing, or corrosion.

4. 4

   Use a multimeter to test the wiring circuit for a short to ground, which is the primary electrical cause for this code.

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical shorts during the repair.

2. 2

   Access the Intake Plumbing

   Locate the intake air humidity sensor on the air intake pipe between the air filter housing and the turbocharger.

3. 3

   Disconnect Harness

   Carefully unplug the electrical connector from the sensor.

4. 4

   Remove Sensor

   Unbolt or unclip the sensor from the intake plumbing.

5. 5

   Clean or Replace

   If the sensor is simply fouled with heavy water droplets, carefully dry it and the connector. If the wiring harness tested fine for shorts but the voltage remains low, the sensor is internally defective and must be replaced.

6. 6

   Install New Sensor

   Insert the new sensor into the intake plumbing and secure it.

7. 7

   Reconnect

   Plug the electrical harness back into the sensor and reconnect the battery.

8. 8

   Clear Codes / Validation Restart

   Use a diagnostic tool to clear the ECU fault codes. If the machine experienced a full power loss or derate (low idle) due to the SCR system fault, you may need to perform an emergency re-start or a validation restart sequence to restore full engine power.