•  Based on the control of the A/F sensor heater and HO2S heater, a stabilized oxygen concentration is detected even at low exhaust gas temperature and feedback control of fuel injection even during cold engine start is made possible for improved cold temperature exhaust emission performance.

•  When exhaust gas temperature is high, the A/F sensor and HO2S are protected from a rise in temperature by the stopping of energization to the A/F sensor heater and HO2S heater.

•  Through duty control of the A/F sensor according to engine operation conditions (emission temperature), both exhaust emission performance improvement and protection of the A/F sensor have been achieved.