New Holland ENG 3549 – Engine Control Unit (ECU) / EDC: Humidity Sensor Signal Ratio failure - Signal Ratio above Limit

The engine control system has detected that the signal coming from the intake air humidity sensor is out of its expected plausible range (reading higher than the acceptable limit).

• T7 Series (T7.220, T7.270)
• T8 Series
• T6 Series
• CR Series (CR6090, CR9090)
• CX8080
• CX8090 Elevation

1. 1

   Check for water ingress in the intake system and look for related informational codes like 3557 or 3558.

2. 2

   Inspect the electrical pigtail and connector at the sensor for corrosion, pushed-out pins, or moisture bridging the connections.

3. 3

   Monitor live data for the humidity sensor and ambient air temperature sensor, comparing readings to actual ambient weather conditions.

1. 1

   Locate the Sensor

   Turn off the engine and remove the key. Locate the humidity sensor, which is mounted on the engine air suction/intake pipe, downstream of the engine air filter.

2. 2

   Disconnect

   Unplug the electrical harness from the sensor.

3. 3

   Remove and Inspect

   Remove the sensor from the intake pipe. Inspect the sensor tip and the inside of the intake tract for physical water droplets, heavy dust buildup, or oil residue.

4. 4

   Dry the Intake (If Applicable)

   If the intake tract is wet, thoroughly dry it and investigate the source of the water entry (e.g., damaged air filter housing, missing rain cap).

5. 5

   Replace the Sensor

   If the wiring is intact, the intake is dry, and the code persists (or the sensor is physically damaged/failed), install a new humidity sensor.

6. 6

   Reassemble and Clear Codes

   Plug the electrical connector back in. Turn on the machine, use a diagnostic tool to clear the inactive ENG 3549 code, and run the engine to verify the code does not return.