Circuit Description

WARNING: This page is about a different car, the 2003 Toyota Tacoma. However, it is still accessible from the selected car via links, so may be relevant.

To obtain a high purification rate of the CO, HC and NOx components of the exhaust gas, a three-way catalytic converter is used. But, for the most efficient use of the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio. The A/F sensor has a characteristic of providing output voltage (the voltage value changes inside ECM only) approximately proportional to the existing air-fuel ratio. The A/F sensor output voltage (the voltage value changes inside ECM only) is used to provide feedback for the ECM to control the air-fuel ratio. By the A/F sensor output, the ECM can determine the deviation amount from the stoichiometric air-fuel ratio and control the proper injection time immediately. If the A/F sensor is malfunctioning, ECM is unable to perform the accurate air-fuel ratio control. The A/F sensor is equipped with a heater which heats the zirconia element. The heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is low), current flows to the heater to heat the sensor for the accurate oxygen concentration detection.