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Discussion Starter · #1 ·
I am in the process of diagnosing a P0420 (that repeatedly came back after erasures) on my 2000 Corolla. It has original O2 sensors and catalytic converters. The MAF sensor was a few year old and cleaned with electrical cleaner a few months ago. It also loses engine oil after driving (around 1 Qt per few hundred miles), but there is visible sign of oil on the out side of the engine, probably due to old gaskets.

I am using a simple scan tool that shows numbers but cannot graph.

The measurements described are taken a few minutes after the engine starts with engine spinning at around 2500 RPM.

- O2 sensor 1 (Is this upstream?) is oscillating between around 0.1V to 0.8V.

- O2 sensor 2 (Is this downstream?) was quite stable around 0.7V and 0.8V (with occasional excursion to low voltages)

Can anyone advice me on how to interpret these findings, especially the sensor 2 reading, and give me an opinion on what could be bad and what other tests I should perform?

Thanks,
 

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マズダスピード3
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15,431 Posts
What brand o2 sensor are you using? Should be using Denso.

Are you able to post freeze frame data?
 

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Discussion Starter · #3 · (Edited)
Hi 75aces,

The o2 sensors are original, so should be Denso.

I have embedded images of my scan tool live data measurements in subsequent posts (can't do freeze frame). Each complete set of live data has three images and there are five sets of live data; all of which are taken within two minutes at around 2500 RPM after the car is driven for about 10 minutes.

Thanks again for helping.
 

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マズダスピード3
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Can your scan tool tell you when the O2 sensor goes in closed loop? Look at the connector for the O2. Do you have 2 or 3 wire connector? I doubt there's a heater wire for this gen.

What do the readings look like when you drive it around? If the value is static, that indicates it's stuck. Not sure if it's in open or closed loop. Oscillating is a good sign.
 

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05 camry 07 tacoma
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With older vehicle if not wanting to change sensors and converter try off setting the after cat sensor to fix P0420.
Lots of info out there on how this is done.

Does error need to be cleared for upcoming smog check?
 
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