Double air-fuel ratio sensor system having improved response characteristics

摘要

In a double air-fuel sensor system including two air-fuel ratio sensors upstream and downstream of a catalyst converter provided in an exhaust gas passage, an actual air-fuel ratio is adjusted in accordance with the outputs of the upstream-side air-fuel ratio sensor and the downstream-side air-fuel ratio sensor. The adjustment of the actual air-fuel ratio by the downstream-side air-fuel ratio sensor is prohibited in accordance with a coolant temperature of the engine.