New Holland ENG 3557 – Engine Control Module (Engine ECU / EDC): Info: Humidity Sensor possibly saturated with water droplets - Signal Ratio above Limit.

The engine's humidity sensor monitors the moisture level of the air entering the engine. This sensor is crucial for calculating raw NOx emissions and managing the SCR (AdBlue/DEF) aftertreatment system's efficiency. Code 3557 triggers when the sensor's signal ratio exceeds the upper limit, which typically happens when the sensor element becomes physically saturated with liquid water droplets due to heavy rain ingress, condensation in the intake, or high-pressure washing.

• T6 series
• T7 series
• T7.220
• T7.270
• T8 series
• T9 series
• T9.700
• CR series
• CR6090
• CR9090
• CX series
• CX8080
• CX8090
• Magnum 235-340 (Series 4)

1. 1

   Check the engine air intake system (air filter housing and piping) for signs of standing water, heavy condensation, or snow/rain ingress.

2. 2

   Locate the humidity sensor on the engine air suction pipe downstream of the air filter.

3. 3

   Disconnect the sensor and inspect the electrical connector and wiring harness for corrosion, trapped moisture, or damaged pins.

4. 4

   Remove the sensor and check if the element is wet. If it is, gently dry the sensor and the surrounding intake pipe.

5. 5

   Look for accompanying codes such as ENG 3558 (Signal Ratio below Limit) or ENG 3561 (NOx value not plausible), which can be triggered by a skewed humidity reading.

1. 1

   Turn off machine

   Turn off the machine, remove the key, and allow the engine to cool.

2. 2

   Locate sensor

   Locate the humidity sensor on the air intake pipe, just after the main air filter housing.

3. 3

   Disconnect harness

   Disconnect the electrical harness connector from the humidity sensor.

4. 4

   Remove sensor

   Unbolt or unclip the humidity sensor from the intake pipe and carefully remove it.

5. 5

   Inspect and dry sensor

   Inspect the sensor tip. If it is simply wet, dry it thoroughly with ambient air (do not use high-pressure compressed air directly on the delicate sensor element).

6. 6

   Inspect and dry intake pipe

   Inspect the intake pipe for excess moisture and dry it out if necessary to prevent immediate re-saturation.

7. 7

   Replace sensor if necessary

   If the sensor is corroded, physically damaged, or if the fault code returns immediately after drying and clearing, the sensor has failed and must be replaced.

8. 8

   Install new sensor

   Install the new humidity sensor into the intake pipe and secure it.

9. 9

   Reconnect harness

   Reconnect the electrical harness.

10. 10

    Clear codes and verify

    Power on the machine and use a CNH diagnostic tool (EST) to clear the inactive fault codes and verify the sensor is reading ambient humidity correctly.