A method for sensing an air-fuel ratio of exhaust gasses from an engine of a vehicle using a sensor is provided. The method may comprise pumping a current in a pumping cell during; reducing said pumping during a set of operating conditions; and adjusting a fuel injection amount or an air amount into the engine to maintain a desired air-fuel ratio based on the sensor. In this way, a reference voltage can be driven by chemical reactions to equilibrate and provide an accurate indication of stoichiometry, similar to a HEGO sensor. Likewise, outside of stoichiometry, the reference voltage is controlled in a one-sided fashion via positive and negative pumping current at respective voltage limits to provide an indication of air-fuel ratio over a wide range.