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Prius 3rd Gen throws P0420, is it a bad Oxygen sensor?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by melvinpmanuel, Jul 14, 2020.

  1. melvinpmanuel

    melvinpmanuel New Member

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    I recently purchased a 2013 Prius with 114000 miles on it. The engine light is ON and I scanned for the code and got P0420 "Catalyst System Efficiency below Threshold bank1". I have gone through our previous threads on similar issues and ended up with culprit Oxygen sensors. I checked the voltages from O2 sensors and O2B1S2(V) = 0.788 and O2B1S1(V) = 3.401 at RPM 2500.

    From our forum, on third-gen Prius, the O2B1S1 is actually an Air Fuel Ratio Sensor (Located backside of the engine, before the catalytic converter, where we need to remove the whole wiper assembly to access it). What is the normal voltage range from this sensor? Some threads it says between 0.6 to 1 V. Some threads it says 3 to 3.8 V. Which one is correct?. Is this an O2 sensor or a AF ratio sensor? Does this sensor cause P0420?

    O2B1S2 sensor, I believe located after the catalytic converter, which we can access easily from the bottom of the car. What should be the normal range of voltage expected from this sensor? Does this cause P0420?

    Also, could anybody share the normal range of values for OBD II Live Data?

    Thanks in advance
    Melvin
     
  2. bisco

    bisco cookie crumbler

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    sorry no one has answered. you should be able to find this data in the service manual. techinfo.toyota.com
     
  3. Robehne

    Robehne Junior Member

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  4. Rebound

    Rebound Senior Member

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    An oxygen sensor error code often is not caused by a faulty oxygen sensor.

    Modern cars work by monitoring air flow and air pressure to determine how much fuel to inject to create the correct stoichiometric ratio for optimal efficiency. The oxygen sensors are used to measure the combustion byproducts to verify that the combustion was correct. If there’s too much or too little oxygen in your exhaust, you’ll get an oxygen sensor light.

    For example, Prius has one oxygen sensor before the catalytic converter, and another after the catalytic converter. If the catalytic converter is malfunctioning, it will trip an oxygen sensor warning, although the oxygen sensor is working correctly.

    Do you have any other diagnostic codes?