What is a normal operating temperature for a 2009 cadillac cts4 because my gage isreading100

The normal operating temperature of a 2009 Cadillac CTS is between about 202 and 239 degrees Fahrenheit. Optimum temperature will probably be between 202 degrees and 220 degrees. 100 degrees is far too low and simply has to be erroneous. Even if the thermostat was sticking open or was missing altogether, the engine would be hotter than 100 degrees after running a bit. You could have a faulty gauge or faulty temperature gauge sending unit. I would recommend a hands on inspection utilizing a diagnostic tool that can monitor temperature and other components.