Focus L4-2.0L SOHC VIN P (2000)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
Cylinder Head Temperature Sensor
Cylinder Head Temperature Sensor
Cylinder Head Temperature (CHT) Sensor
The Cylinder Head Temperature (CHT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a
thermistor decreases as temperature increases, and increases as temperature decreases. The varying resistance affects the voltage drop across the
sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of
the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal
to the reference voltage minus the voltage drop across the fixed resistor.
The Cylinder Head Temperature (CHT) sensor is installed in the aluminum cylinder head and measures the metal temperature. The CHT sensor
communicates an overheating condition to the PCM. The PCM would then initiate a cooling strategy based on information from the CHT sensor. A
cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components
could occur. Using a CHT sensor and cooling strategy would prevent damage by allowing air cooling of the engine and limp home capability.
