Pcm Code P073 - Intermittent Coolant Temp Sensor Signal: Notes
WARNING: This page is about a different car, the 1993 Cadillac Seville and 1993 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
Coolant Temperature Sensor (CTS) 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 CTS voltage. If PCM detects a large change in sensor output voltage in a one-second period, code will set.