New Holland ENG 3518 – Engine Control Unit (ECU): Air Filter Temperature Sensor: Ambient Air Temperature Sensor failure (of Humidity Sensor if installed) - Signal too low

The Engine Control Unit (ECU) is receiving a voltage signal from the ambient air temperature/humidity sensor that is below the acceptable minimum threshold. This typically points to a short to ground in the sensor's wiring circuit, a damaged harness, or an internal failure of the sensor itself.

• L220
• SR175
• B90B
• B100B
• W50C
• W60C
• W70C
• W80C
• W110C
• T6
• T7
• T8
• T9
• Magnum (235-340)

1. 1

   Locate the Ambient Air Temperature / Humidity sensor on the engine air suction/intake pipe, directly downstream of the main air filter.

2. 2

   Inspect the sensor connector and the wiring harness leading back to the Engine ECU for chafed wires, melted insulation, or pinched harnesses that could cause a short to ground.

3. 3

   Disconnect the sensor and turn the key to the ON position. Use a multimeter to verify the 5V reference voltage and the ground circuit at the connector.

4. 4

   If the reference voltage is missing, check for continuity between the sensor connector and the ECU pins to rule out a broken wire.

5. 5

   If the wiring harness is intact, free of shorts, and delivering the correct voltage, the sensor has failed internally and must be replaced.

1. 1

   Disconnect battery

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Locate sensor

   Open the engine cowling and locate the air intake piping immediately after the air filter housing.

3. 3

   Disconnect sensor harness

   Depress the locking tab on the electrical connector and carefully unplug the harness from the Humidity/Ambient Air Temperature Sensor.

4. 4

   Remove faulty sensor

   Remove the faulty sensor from the intake pipe. Depending on the exact engine model, it will either unthread or be held in place by a retaining screw/clip.

5. 5

   Install new sensor

   Install the new sensor into the intake pipe. Do not overtighten if it is a threaded plastic sensor.

6. 6

   Reconnect harness

   Reconnect the electrical harness, ensuring the locking tab clicks securely into place.

7. 7

   Reconnect battery

   Reconnect the negative battery cable.

8. 8

   Clear fault codes

   Turn the ignition on. Use a CNH Electronic Service Tool (EST) to clear the inactive fault codes, or cycle the key to verify that ENG 3518 changes from 'Active' to 'Inactive'.