Circuit Description

ECT sensor circuit uses 2 pull-up resistors for temperature sensing. When sensor resistance is high, indicating low temperature, the PCM uses a 3650 ohms resistor and a 348 ohms resistor in series. As temperature increases to 122°F (50°C), the sensor resistance will decrease to 973 ohms. This resistance corresponds to .97 volt at the PCM. At this point the PCM shifts to the single 348 ohms pull-up resistor to measure temperature at greater than 122°F (50°C).

The PCM monitors the voltage signal of the circuit and assumes that engine operation causes coolant temperatures to change at slow rates. This test monitors the ECT sensor voltage. If PCM detects a large change in sensor output voltage in a one second period, DTC will set.