Circuit Description

WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.

This DTC is recorded when A/F sensor has a malfunction, although the caption is heated oxygen sensor. The air-fuel ratio sensors are the lamination type. Compared to the conventional type, the sensor and heater portions of the lamination type are narrower overall. Because the heat of the heater acts directly on the alumina and zirconia part of the sensor, it accelerates the activation of the sensor. To obtain a high purification rate of the CO, HC and NOx components in the exhaust gas, a three-way catalytic (TWC) converter is used. For the most efficient use of the TWC, 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 the ability to provide output voltage. (The voltage value changes at the inside of the ECM only and is approximately proportional to the existing air-fuel ratio). The A/F sensor output voltage 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 out of order, 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), the current flows to the heater to heat the sensor for the accurate oxygen concentration detection.