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Engine Controls - A/F And O2 Sensor Identification|Page 693 > < Engine Controls - A/F And O2 Sensor Identification|Page 691

Highlander 2WD L4-2.4L (2AZ-FE) (2001)

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Oxygen Sensor: Description and Operation

Heated Oxygen Sensor

The ECM observes the waveform of the heated oxygen sensor located behind the catalyst to determine whether the catalyst performance has deteriorated.

If the catalyst is functioning normally, the waveform of the heated oxygen sensor located behind the catalyst switches back and forth between rich and
lean much more slowly.

When the waveform of the heated oxygen sensor located behind the catalyst alternates flutteringly between rich and lean, it indicates that catalyst
performance has deteriorated.

Air / Fuel Sensor

To obtain a high purification rate for 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 the characteristic that provides output voltage* approximately proportional to the existing air-fuel ratio. The A/F sensor output

Engine Controls - A/F And O2 Sensor Identification|Page 693 > < Engine Controls - A/F And O2 Sensor Identification|Page 691