Case IH 3679 – Engine Control Unit (ECU) / EDC (Electronic Diesel Control): Temperature sensors : over plausible temperature

One of the engine's temperature sensors is reporting a thermal value that is higher than physically possible or expected. This typically indicates a short circuit to power, a short circuit to ground, or a completely failed thermistor inside the sensor.

• Case IH Farmall
• Case IH Maxxum
• Case IH Puma

1. 1

   Connect the CNH EST or EASy diagnostic tool and monitor live data for Engine Coolant, Fuel, Intake Air, and Exhaust Gas Temperature sensors to identify which is reading implausibly high.

2. 2

   Inspect the identified sensor's wiring harness and connector for corrosion, chafing, or melted wires that could cause a short circuit.

3. 3

   Perform a disconnect test: unplug the sensor. If the diagnostic reading drops to a default minimum, the wiring harness is likely intact and the sensor has failed.

4. 4

   Perform a resistance test using a multimeter across the sensor pins. A reading of near-zero ohms indicates an internal short.

1. 1

   Identify the Sensor

   Use the diagnostic tool to pinpoint the exact temperature sensor causing the fault.

2. 2

   Prep the Machine

   Turn off the engine, remove the key, and disconnect the battery. If replacing the coolant temperature sensor, allow the engine to cool completely and drain the coolant below the level of the thermostat housing/water jacket.

3. 3

   Remove the Faulty Sensor

   Disconnect the electrical connector. Use a wrench to carefully unscrew the faulty temperature sensor from its housing.

4. 4

   Install the New Sensor

   Thread the new OEM sensor into the housing. Tighten to the manufacturer's specified torque to avoid damaging the brass threads or the housing.

5. 5

   Reconnect and Refill

   Reconnect the electrical harness. If you drained coolant, refill the system and bleed any air.

6. 6

   Clear Codes and Test

   Reconnect the battery, use the CNH EST tool to clear the 3679 fault code, and run the engine under load to verify the temperature readings are now within normal, plausible parameters.