Case IH 3557 (DTC FB54) - ECU – Engine Control Unit (ECU): Intake air humidity sensor voltage is higher than expected

The intake air humidity sensor is sending a voltage signal back to the controller that exceeds the maximum expected threshold. This is typically caused by the sensor being physically saturated with water droplets, a short circuit to an external power source in the wiring, or a failed sensor.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Magnum Series (235–380)
• Steiger Series
• Puma Series
• Farmall models with CVT transmissions

1. 1

   Remove the sensor and inspect the intake air plumbing for excessive moisture, water ingress, or condensation (sensor may be saturated with water droplets)

2. 2

   Disconnect the sensor and inspect the electrical connector pins for water, corrosion, or debris

3. 3

   Test the sensor wiring harness for a short circuit to an external power source (signal wire shorted to power)

1. 1

   Power Down

   Turn off the machine and turn off the battery disconnect switch.

2. 2

   Locate the Sensor

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

3. 3

   Clear Moisture

   If water droplets are found in the intake tract or on the sensor, dry the sensor tip carefully and wipe out the intake tubing.

4. 4

   Test/Clear Code

   Reinstall the dried sensor, reconnect the harness, power on the machine, and check if the code moves to an inactive state.

5. 5

   Replace Sensor

   If the wiring harness tests good (no shorts to power) and the sensor is completely dry but the 3557 / FB54 code remains active, the sensor has failed internally and must be replaced.

6. 6

   Install New Part

   Install the new intake air humidity sensor into the intake plumbing, plug in the connector, and clear the fault codes via the diagnostic menu or service tool. Run the engine to verify the code does not return.