Case IH 3940 – Engine Control Module (ECM) / Engine Control Unit (ECU): ECU Temperature Sensor: Physical Signal ECU Temperature second sensor below minimum limit

The secondary internal temperature sensor located on the circuit board inside the Engine Control Unit (ECU) is reporting a temperature value that has dropped below the minimum allowable operating threshold.

• Case IH and New Holland agricultural equipment (tractors, combines, and floaters) equipped with CNH EDC Tier 3 and Tier 4a engine systems

1. 1

   Verify the ambient temperature to determine if the machine is operating in extreme cold, which can cause accurate below-minimum readings.

2. 2

   Check the main power and ground supplies to the Engine Control Module for voltage drops or poor grounds that can skew internal sensor reference voltages.

3. 3

   Look for related internal ECU faults, such as 3939 (second sensor above maximum limit), 3942 (Diagnostic Fault Check for Signal below minimum limit), or SPI communication errors.

1. 1

   Warm the Environment

   If the tractor is in deep freeze conditions, move it to a heated shop or allow the engine block heater to warm the engine bay. Clear the code and cycle the key to see if the fault returns.

2. 2

   Inspect the Harness

   Disconnect the main harnesses to the ECM and inspect the pins for corrosion, moisture intrusion, or pushed-out pins that could cause voltage drops.

3. 3

   Clear and Retest

   Use the CNH Electronic Service Tool (EST) to clear the fault codes. If code 3940 immediately returns as an active fault at normal room temperature, the internal sensor has failed.

4. 4

   Replace the ECM

   Because the internal temperature sensor cannot be serviced separately, a persistent 3940 code indicates a critical internal hardware failure. You must remove and replace the entire Engine Control Module.

5. 5

   Reprogram the Module

   Install the new ECM and flash it with the latest firmware using the CNH diagnostic software to ensure compatibility with the machine.