Code P073, Intermittent Engine Coolant Temp Sensor Signal: Notes
WARNING: This page is about a different car, the 1995 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
Engine Coolant Temperature (ECT) sensor circuit uses 2 pull-up resistors for temperature sensing. When sensor resistance is high (indicating low temperatures), PCM uses 3.65-k/ohm resistor and 348-ohm resistor in series. As temperature increases to 122°F (50°C), sensor resistance will decrease to 973 ohms. This resistance corresponds to .97 volt at PCM. At this point PCM shifts to single 348-ohm pull-up resistor to measure temperature greater than 122°F (50°C).
PCM monitors voltage signal of circuit and assumes engine operation causes coolant temperatures to change at slow rates. This test monitors ECT sensor voltage. If PCM detects a large change in sensor output voltage in a one-second period, code will set.