Case IH F-171-01 - ECU – Engine Control Unit (ECU): Ambient temperature sensor voltage is lower than expected

The signal voltage from the ambient air temperature sensor has dropped below the minimum acceptable threshold, indicating a short circuit to ground, a damaged wiring harness, or an internally failed sensor.

• MAGNUM AFS Connect
• Case IH 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Case IH Magnum Series (235 - 340 Series 4)
• STX Steiger Series (350 to 600 HP)
• Farmall Series (40-45-50 models with Cab and CVT)
• CVX Series
• Case IH N Series Loaders
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL) equipped with F5C engines

1. 1

   Verify the active fault code (often displayed as DTC 3518 or 2AC4) using the machine's Electronic Service Tool (EST) or in-cab diagnostic display

2. 2

   Inspect the ambient air temperature sensor, its connector, and the wiring harness for physical damage, moisture, or corrosion

3. 3

   Test the sensor circuit for a short to ground between the sensor and the ECU

1. 1

   Power down the machine

   Power down the machine and turn off the battery disconnect switch.

2. 2

   Locate the sensor

   Locate the ambient air temperature sensor. It is usually mounted somewhere in the airstream (often near the intake or cab exterior) but protected from direct impact.

3. 3

   Disconnect the old sensor

   Disconnect the old sensor by unplugging it from the existing wiring harness.

4. 4

   Remove the sensor

   Unclip or unbolt the sensor from its mounting location.

5. 5

   Install the new sensor

   Install the new direct-replacement sensor into the mounting location.

6. 6

   Connect the wiring harness

   Plug the wiring harness into the new sensor, ensuring the connector clicks securely into place.

7. 7

   Restore power and test

   Restore battery power, clear the fault codes from the ECU, and test the engine and climate control operation to ensure the system responds correctly to outside conditions.