Heated Oxygen Sensor (HO2S)

All vehicles except Sonata 2.5L are equipped with 2 Heated Oxygen Sensors (HO2S). Sonata 2.5L is equipped with 4 sensors, one pair for each bank. On all models, a front HO2S is located in the exhaust manifold in front of the catalytic converter. The front HO2S determines whether the air fuel mixture is too rich or too lean. ECM uses front HO2S to control air fuel mixture and fuel delivery time. A rear HO2S is located after the catalytic converter. ECM compares signals from both sensors and calculates catalytic converter efficiency. On all models except Sonata 2.5L, HO2S output voltage ranges from 0-0.1 volt (lean) to about 0.8-1.0 volt (rich). On Sonata 2.5L, HO2S output voltage ranges from 0-0.2 volt (lean) to about 4.5-5.0 volts (rich). HO2S heater is used to bring sensor to operating temperature as quickly as possible for optimum operation under all engine operating conditions.