Case IH 1547-04 - BCM – BCM: A/C Evaporator Temperature Sensor - Voltage Below Normal / Out of Range Low

The controller is detecting that the voltage from the A/C evaporator core temperature sensor has dropped below 0.1 VDC, indicating that the sensor's electrical resistance has dropped below 52 Ohms. This mimics an impossibly high temperature reading and is almost always caused by a short to ground in the sensor wiring or an internal short inside the sensor itself.

• MAGNUM AFS Connect
• 2144
• 2166
• 2188
• 2344
• 2366
• 2377
• 2388
• 2577
• 2588
• 5088
• 6088
• 7088
• 2155
• 2555
• CPX420
• CPX610
• CPX620
• MX285
• MX305
• Magnum Series
• Puma Series (130-240)
• Maxxum Series (115-150)

1. 1

   Disconnect the evaporator temperature sensor and measure its resistance with a multimeter (less than 52 Ohms at room temperature indicates an internal short).

2. 2

   Check the signal wire between the sensor connector and the BCM/ATC for a short to ground.

3. 3

   Compare the evaporator temperature sensor resistance with the return air sensor at the same ambient temperature (they should have identical resistance-to-temperature values).

4. 4

   Check cab grounds, specifically the HVAC ground, ensuring resistance is less than 1 ohm from the battery post to the frame.

1. 1

   Access the HVAC Plenum

   Locate the HVAC evaporator box. On many Case IH tractors (like the MX series), this requires raising or removing the seat to access the divider between the HVAC plenum and the electrical distribution area. On combines, access the cab roof or external HVAC blower box.

2. 2

   Inspect the Wiring

   Visually inspect the harness leading to the sensor for chafing against the frame or evaporator housing, which is the most common cause of a 'short to ground' (FMI 04) fault.

3. 3

   Remove the Faulty Sensor

   Unplug the sensor connector. Carefully pull the temperature sensor probe out of the evaporator core fins.

4. 4

   Install the New Sensor

   Gently insert the new sensor probe into the exact same location in the evaporator core fins. Ensure it is seated deeply enough to accurately read the core temperature to prevent freezing.

5. 5

   Secure the Harness

   Use cable ties (OEM strap part # 702093C1) to secure the sensor wire away from moving blower parts or sharp edges.

6. 6

   Clear Codes and Test

   Turn the key on, clear the BCM fault codes, and run the A/C system. Verify that the compressor clutch cycles properly and the evaporator does not freeze over.