ASE A1 Engine RepairLubrication and Cooling SystemsEasy
A technician is diagnosing a vehicle with a persistent overheating issue. The engine temperature gauge consistently reads high, and the coolant reservoir is boiling. After inspecting the system, the technician finds that the radiator cooling fan is not activating when the engine reaches operating temperature. Which of the following is the MOST likely cause?
- AA clogged heater core
- BA leaking water pump
- CA stuck-open thermostat
- DA faulty engine coolant temperature (ECT) sensor
Show answer & explanationAnswer & explanation
Correct answer: D. A faulty engine coolant temperature (ECT) sensor
The ECT sensor provides crucial temperature data to the engine control unit (ECU), which then signals the cooling fan to activate. If the sensor is faulty, the ECU may not receive the correct temperature information, preventing the fan from turning on and leading to overheating.
Why the other options are wrong
- A. A clogged heater core would primarily affect cabin heat and might cause slight overheating, but wouldn't directly prevent the cooling fan from activating.
- B. A leaking water pump would lead to coolant loss and overheating, but the fan should still attempt to run if the ECT sensor is functional.
- C. A stuck-open thermostat would cause the engine to run cold, not overheat, and would not directly affect fan operation.
Engine Coolant Temperature (ECT) Sensor
A thermistor that measures engine coolant temperature and sends this data to the engine control unit (ECU).
- Crucial for fuel injection, ignition timing, and cooling fan control.
- Sends a voltage signal that changes with temperature.
- Failure can lead to poor performance, rich/lean conditions, or overheating.
Memory trick: Temperature tells the Computer to turn the Fan.