Heated Oxygen Sensors

The front Heated Oxygen (HO2S) sensor determines whether the air fuel mixture is too rich or too lean. It generates a voltage signal depending on oxygen content in exhaust gases. ECM uses inputs from front HO2S for calculating fuel mixture correction to fuel injector pulse width. Front HO2S is located before warm-up catalytic converter. ECM uses input from rear HO2S to monitor effectiveness of Three Way Catalytic (TWC) converter. Rear HO2S is located downstream from TWC converter.