Case IH 3008 (F-4076-04) – Engine Control Unit (ECU): Engine coolant temperature sensor voltage is lower than expected

The voltage signal returning from the engine coolant temperature sensor to the controller has dropped below the minimum acceptable threshold. This condition is typically caused by the sensor signal circuit being shorted to ground, an open circuit in the sensor supply connection, or an internal failure of the sensor itself.

• VESTRUM CVX
• 240 Series Axial-Flow Combines
• Magnum 235 - 340 (Series 4)
• Farmall 40-45-50
• Puma Series
• Austoft 9900

1. 1

   Verify Active Status: Use the Electronic Service Tool (EST) to verify if the fault code is currently active or stored as an inactive history code.

2. 2

   Wiring Harness Inspection: Inspect the wiring harness between the coolant temperature sensor and the Engine ECU. Specifically, test the signal circuit for a short to ground.

3. 3

   Supply Voltage Check: Check the sensor supply connection to ensure it is not open or shorted to ground.

4. 4

   Connector Check: Inspect the 2-pin connector at the sensor for water intrusion, corrosion, or pushed-out pins.

1. 1

   Access the Sensor

   Locate the engine coolant temperature sensor, which is typically threaded into the engine block or cylinder head near the thermostat housing.

2. 2

   Disconnect and Inspect

   Unplug the 2-pin electrical connector from the sensor.

3. 3

   Test the Circuit

   With the sensor unplugged, turn the key ON (engine OFF) and check the voltage at the harness connector to rule out a wiring short to ground.

4. 4

   Replace the Sensor

   If the wiring tests good (no shorts to ground and proper reference voltage is present), the sensor has failed internally. Unthread the old sensor and install the new one. (Note: Have the new sensor ready or drain the coolant partially to prevent excessive coolant loss during swapping).

5. 5

   Clear Codes

   Reconnect the harness, top off the engine coolant if any was lost, and use the EST to clear the fault code. Run the engine to verify the code does not return.