•  Stabilized oxygen concentrations, even when the exhaust gas temperature is low, are detected by controlling of the A/F sensor and HO2S, enabling feedback control of the fuel injection control even during cold-engine starting, improving emission performance when cold.

•  When the exhaust gas temperature is high, the A/F sensor and HO2S is protected from sharp rises in its temperature by stopping energization to the A/F sensor and HO2S heater.

•  Emission performance improvement and protection of the A/F sensor and HO2S have both been achieved by the duty control of the A/F sensor and HO2S according to the engine operation conditions (exhaust gas temperature).