Case IH 3006 – Engine Control Unit (ECU): Coolant Temperature Sensor - Signal Not Plausible (Compared with Engine Oil Temperature)

The engine's computer continuously monitors both the engine coolant temperature and the engine oil temperature. During normal operation (and especially during a cold start), these two temperature readings should correlate within a specific expected range. If the coolant temperature reading deviates significantly from the oil temperature reading, the system flags the coolant sensor's signal as "implausible" or invalid. This typically points to a failing coolant temperature sensor, a wiring harness issue, or a stuck thermostat preventing the coolant from warming up properly.

• Case IH Magnum Series (e.g., 235–340 Series 4)
• Case IH STX Steiger Series (350 to 600 HP models)
• Case IH Farmall Series
• Case IH Puma Series
• Case IH Combines (e.g., 7120, 8010, 9240)
• Case IH Patriot Sprayers

1. 1

   Live Data Comparison: Connect a diagnostic scan tool (such as the Case IH EST or Jaltest) and view the live data for both the Coolant Temperature and Engine Oil Temperature.

2. 2

   Cold Soak Test: Let the tractor sit overnight. Before starting the engine, check the live data. Both the coolant and oil temperature sensors should read the same (ambient) temperature. If the coolant sensor reads artificially high or low, the sensor is likely faulty.

3. 3

   Wiring Inspection: Inspect the wiring harness and connector at the coolant temperature sensor. Look for chafed wires, corrosion, or moisture inside the connector that could skew the resistance signal.

4. 4

   Thermostat Check: Ensure the engine is actually reaching operating temperature. If the thermostat is stuck open, the coolant will remain cold while the oil heats up, which can also trigger a plausibility fault.

1. 1

   Power Down

   Turn off the machine and engage the master battery disconnect switch to prevent electrical shorts.

2. 2

   Locate the Sensor

   Locate the coolant temperature sensor, typically threaded into the engine block, cylinder head, or thermostat housing (location varies by specific NEF/QSM engine model).

3. 3

   Disconnect

   Unplug the electrical connector from the sensor.

4. 4

   Remove Sensor

   Place a catch pan under the work area to catch any escaping coolant. Use a deep socket or wrench to carefully unthread and remove the faulty coolant temperature sensor.

5. 5

   Install New Sensor

   Thread the new OEM coolant temperature sensor into the housing. Tighten to the engine-specific torque specification (do not overtighten, as these are often brass fittings).

6. 6

   Reconnect

   Plug the electrical harness back into the sensor, ensuring it clicks and locks into place.

7. 7

   Refill Coolant

   Top off the engine coolant reservoir to replace any fluid lost during the swap.

8. 8

   Clear Codes and Test

   Reconnect the battery, connect your diagnostic tool, and clear fault code 3006. Start the engine and let it reach normal operating temperature to verify the code does not return and that the live data matches expected values.