Not all of the sensor malfunctions will show ERROR CODES, for example a CTS sensor will never show as faulty as it does not have a range that can be exceeded even when at fault, ie it(ECM) assumes it gets a reading and all is well, it does not know reading is out, as it has not been told to ignore anyting below or over a certain amount.
If you are getting a mix for a very cold engine at -10c but when it is ACTUALLY FULLY WARM IN SUMMER HEAT it does not know this.
I have one but have never used it, I beleive it does not work on later FORD ECM, only earlier Weber Marelli ones.
CTS is MAIN CORRECTIVE FACTOR FOR CO, so vital.
tabetha