Case IH 3558 – Engine Control Unit (ECU) / EDC (Electronic Diesel Control): Info: Humidity Sensor possibly saturated with water droplets - Signal Ratio below Limit

This is an informational diagnostic code indicating that the engine's intake air humidity sensor is outputting a signal ratio that has fallen below its minimum expected operational threshold. The system interprets this specific signal drop as the sensor element being physically covered in liquid water (such as condensation, rain ingress, or snowmelt) rather than simply measuring high atmospheric humidity.

• Magnum Series (235, 260, 290, 315, 340 - Series 4)
• Steiger Series
• Puma Series
• Optum Series

1. 1

   Determine if the machine has recently been operated in heavy rain, dense fog, blowing snow, or if it was recently pressure-washed, which can force water into the intake.

2. 2

   Inspect the air intake snorkel, pre-cleaner, and air filter housing for standing water or excessive moisture.

3. 3

   Remove and inspect the engine air filters. If the filters are wet, the source of the water ingress must be addressed to prevent engine damage.

4. 4

   Locate the humidity sensor in the air intake tract (between air filter housing and intercooler/turbocharger). Remove the sensor and check for visible water droplets, dirt buildup, or corrosion on the sensor element and the electrical connector pins.

1. 1

   Power Down

   Turn off the engine and engage the battery disconnect switch.

2. 2

   Dry the System

   If water is found in the intake or on the sensor, thoroughly dry the intake tract. Allow the humidity sensor to air-dry naturally in a warm environment. Note: Do not use high-pressure compressed air directly on the delicate sensor element, as this can destroy it.

3. 3

   Clear and Retest

   Reinstall the dried sensor, reconnect the harness, and restore battery power. Use the CNH Electronic Service Tool (EST) or the in-cab diagnostic menu to clear the inactive fault code. Run the engine to see if the code returns.

4. 4

   Replace if Failed

   If the code remains active after the sensor is completely dry, or if the sensor element is visibly corroded or contaminated with dirt/oil, the sensor has suffered permanent drift/failure and must be replaced.

5. 5

   Replacement

   Disconnect the electrical harness, remove the mounting fasteners securing the sensor to the intake pipe, and pull the sensor out. Insert the new OEM humidity sensor (ensuring the sealing O-ring is properly seated to prevent unmetered dust entry), tighten the fasteners, and reconnect the harness.