Monitor Description

The vehicle is equipped with two heated oxygen sensors. One is mounted upstream from the TWC (Three Way Catalytic) converter (Front Oxygen Sensor, "sensor 1"), the second is mounted downstream (Rear Oxygen Sensor "sensor 2"). The catalyst efficiency monitor compares the sensor 1 and sensor 2 signals in order to calculate TWC ability to store the oxygen.

During normal operation, the TWC stores and releases oxygen as needed. This results in low oxygen variations in the post TWC exhaust stream as shown below.

Fig 1: Identifying Waveform Of Heated Oxygen Sensor

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: Identifying Heated Oxygen Sensor Signal Length

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 3: DTC P0420 & P0430 Chart

NOTE:

Bank 1 refers to the bank that includes cylinder No.1.
Bank 2 refers to the bank that does not include cylinder No.1.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.