Engine Temperature Sensor: Description and Operation

The CHT sensor:

^ is mounted into the back of the left cylinder head and is not connected to any coolant passages.
^ sends a signal to the PCM indicating the cylinder head temperature.
- If the temperature exceeds approximately 121°C (260°F), the PCM disables some fuel injectors. The PCM will alternate which fuel injectors are disabled every 24 engine cycles. The cylinders that are not being fuel injected act as air pumps to aid in cooling the engine.
- If the temperature exceeds approximately 166°C (330°F), the PCM disables all of the fuel injectors until the engine temperature drops below approximately 124°C (260°F).

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.