Heated Oxygen Sensor (HO2S)

HO2S produces a small electrical voltage (0-1 volt) when exposed to heated exhaust gas. HO2S is electrically heated for faster warm-up. Heating element is powered through Auto Shutdown (ASD) relay.

HO2S acts like a rich/lean (air/fuel ratio) switch by monitoring oxygen content in exhaust gas. This information is used by PCM to adjust air/fuel ratio by adjusting injector pulse width.

HO2S produces low voltage when oxygen content in exhaust gas is high. When oxygen content in exhaust gas is low, HO2S produces a higher voltage. OBD-II system uses a second HO2S after catalytic converter to monitor converter efficiency.