Cylinder Head Temperature Sensor

Cylinder Head Temperature (CHT) sensor is mounted in an aluminum cylinder head and measures metal temperature. CHT sensor is a thermistor which changes resistance proportionate to temperature changes. Resistance increases as cylinder head temperature decreases and decreases as cylinder head temperature increases. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus the voltage drop across the fixed resistor. If CHT sensor signal indicates an overheating condition, PCM will initiate a fail-safe cooling strategy based on information from CHT sensor. For additional information, see FAIL-SAFE COOLING STRATEGY  under POWERTRAIN CONTROL SOFTWARE. Using both CHT sensor and fail-safe cooling, PCM prevents damage by allowing air cooling of engine and limp home capability.