The average scan tool live data stream is typically not quick enough to display detailed data when voltage oscillation is high; such as with a working oxygen sensor. We'd recommend using a digital multi-meter and testing your Ford Mustang's oxygen sensors directly.
A properly functioning oxygen sensor's (front sensor) voltage should be switching between 0.1 to 1.0 volt at a rate of approximately 50 cycles per minute. An O2 sensor voltage above 0.45 volts is interpreted by the ECM as a rich exhaust, and an O2 sensor voltage signal below 0.45 volts as a lean exhaust. Check for quick voltage switching also. Over time an oxygen sensor make become "lazy". Your Ford might not be running the CAT monitor because the O2 voltages do not meet the trip criteria.
Remember also, the rear oxygen sensor should be producing a steady stream of .45 volts (approx.), indicating the catalytic converter is doing it's job.
The Ford drive cycle required to run the Catalyst Efficiency Monitor involves driving your Ford Mustang in stop & go traffic conditions. Include five different constant cruise speeds, ranging from 25 to 45 MPH over a 10 minute period.
