E 150 V8-4.6L SOHC VIN W (2004)
Engine Temperature Sensor: Description and Operation
CYLINDER HEAD TEMPERATURE SENSOR
Typical Cylinder Head Temperature (CHT) Sensor
The cylinder head temperature (CHT) sensor (Figure 32) 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 can
provide complete engine temperature information and can be used to infer coolant temperature. If the CHT sensor conveys an overheating condition to
the PCM, the PCM would then initiate a fail-safe 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 both the CHT sensor
and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp home capability. For additional information,
refer to Powertrain Control Software for Fail-Safe Cooling Strategy details.
