Case IH F-354-31 - ECU – Engine Control Unit (ECU): Intake air humidity sensor voltage is higher than expected

The intake air humidity sensor monitors the humidity and temperature of the incoming air. The Engine Control Unit (ECU) uses this data to estimate raw engine NOx production and properly adjust the amount of Diesel Exhaust Fluid (DEF)/AdBlue injected into the exhaust system. A "voltage higher than expected" condition typically indicates that the sensor is short-circuited to an external power source, the sensor has failed, or there is an accumulation of water droplets on the sensor element.

• MAGNUM AFS Connect
• 240 Series (Axial-Flow)
• Magnum series (250-380)
• Farmall series

1. 1

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

2. 2

   Remove the sensor and inspect it for water droplets, as moisture accumulation can cause the signal value to spike above the maximum limit.

3. 3

   Check the sensor's electrical connector and wiring harness for a short circuit to an external voltage source (SRC high) or damaged pins.

4. 4

   Verify that there are no disturbed CAN signal transmission messages between the sensor and the ECU.

1. 1

   Turn off the machine, lower all implements, and disconnect the battery to ensure safety.

2. 2

   Locate the intake air humidity sensor in the air intake plumbing (between the air filter housing and the turbocharger).

3. 3

   Disconnect the electrical harness from the sensor. Inspect the connector for corrosion, moisture, or damaged wires.

4. 4

   Remove the sensor from the intake plumbing.

5. 5

   If water droplets are present inside the intake tract or on the sensor, dry the sensor and the plumbing. Reinstall the sensor and test the machine.

6. 6

   If the wiring is intact, no moisture is present, and the fault code persists, the sensor is internally shorted/defective and must be replaced.

7. 7

   Install the new intake air humidity sensor into the plumbing.

8. 8

   Reconnect the electrical harness.

9. 9

   Reconnect the battery, turn the key to the ON position, and use a diagnostic tool to clear the F-354-31 fault code from the ECU.

10. 10

    Start the engine and monitor the system to ensure the fault code does not return and that the DEF dosing system operates normally without triggering emergency power loss/derate modes.