was driving along today and noticed the check engine light on on dashboard while on motorway at around 70-80, got home and read the fault codes and it flagged up code 32 A/F Sensor #1 System and A/F Sensor #2 System, what sensor is the a/f sensor and where is it located

the car has a full de-cat and is a bit thirsty ove the last 2 months, would this be due to the fault code or the de-cat

thanks
matt