Circuit/System Description

WARNING: This page is about a different car, the 2018 Buick Encore. However, it is still accessible from the selected car via links, so may be relevant.

When the engine is started, the ECM operates in an open loop mode, ignoring the HO2S signal voltage while calculating the air to fuel ratio. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 40 to 1050 mV. Once sufficient HO2S voltage fluctuation is observed by the ECM, closed loop is entered. The control module uses the HO2S voltage to determine the air to fuel ratio. An HO2S voltage that increases toward 1000 mV indicates a rich fuel mixture. An HO2S voltage that decreases toward 0 mV indicates a lean fuel mixture.

The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter closed loop earlier and the control module to calculate the air to fuel ratio sooner.