can anyone explain how the 02 sensors work as im having problems with them. when the car is plugged in there are no trouble codes present but on live data it says that both sensors b4 and after cat are not ready checked wiring and fuses and all ok. local dealer says they have never come accross the problem b4. history = the car bought with snapped belt replaced 4 valves= engine fires up straight away but idles iraticly revs up ok my thinking = because the o2 sensors are not sending readings back then the car cant adjust the fuel/air mixture c5 2litre petrol y reg 90k