O2 sensors
Thread Starter
Joined: Feb 2003
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From: My little world
O2 sensors
I’m reading my O2 sensors and I’m told the sensor needs to read 4.5v on average. My sensor is technically averaging 4.5 however it’s doing so by going from .08 to .8 v in an alternating pattern. Does that indicate a bad sensor?
Out of all the things I’ve done, I’ve never had to replace o2 sensors. I’m not sure if they should remain around the average voltage or if the average can be achieved over a large sweeping range.
The one i’m having issue with is O2s11. My O2s12 is doing it as well, but only on occasion. I’m diagnosing a po420 code and it is supposed to be downstream sensor or bad cat. Which one of those 2 are downstream?
I’ve rebuilt every inch of my car, twice.... but never had to bother with o2 sensors until now. Trying to learn them.
Out of all the things I’ve done, I’ve never had to replace o2 sensors. I’m not sure if they should remain around the average voltage or if the average can be achieved over a large sweeping range.
The one i’m having issue with is O2s11. My O2s12 is doing it as well, but only on occasion. I’m diagnosing a po420 code and it is supposed to be downstream sensor or bad cat. Which one of those 2 are downstream?
I’ve rebuilt every inch of my car, twice.... but never had to bother with o2 sensors until now. Trying to learn them.
Lexus Test Driver
Joined: Apr 2008
Posts: 1,058
Likes: 126
From: Illinois
Im assuming its your SC400
Lets start with your P0420 code:
Catalyst System Efficiency Below Threshold on Bank 1 (Driver side)
This means your air−fuel ratio waveform of the oxygen sensor before the catalyst repeatedly changing back and forth from rich to lean.
Rich = higher voltage ( ~0.8v) Lean = low voltage ( ~0.3v) about 0.5v fluctuations.
If the catalyst is functioning normally, the waveform of the oxygen sensor after the catalyst switches back and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the catalyst.
But when both waveform change at a similar rate, it indicates that catalyst performance has deteriorated.
Not sure how to read your scanner but it looks like:
O2S11 - Bank 1 Sensor 1 -- before cat
O2S12 - Bank 1 Sensor 2 -- after cat
I'd check exhaust leaks around the O2 sensors, if no leaks found, your cat on Bank 1 is failing.
4.5 volts?
Dont know about that.
Oxygen sensors read max is .9 -1.0 volts when RICH.
Lets start with your P0420 code:
Catalyst System Efficiency Below Threshold on Bank 1 (Driver side)
This means your air−fuel ratio waveform of the oxygen sensor before the catalyst repeatedly changing back and forth from rich to lean.
Rich = higher voltage ( ~0.8v) Lean = low voltage ( ~0.3v) about 0.5v fluctuations.
If the catalyst is functioning normally, the waveform of the oxygen sensor after the catalyst switches back and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the catalyst.
But when both waveform change at a similar rate, it indicates that catalyst performance has deteriorated.
Not sure how to read your scanner but it looks like:
O2S11 - Bank 1 Sensor 1 -- before cat
O2S12 - Bank 1 Sensor 2 -- after cat
I'd check exhaust leaks around the O2 sensors, if no leaks found, your cat on Bank 1 is failing.
4.5 volts?
Dont know about that.
Oxygen sensors read max is .9 -1.0 volts when RICH.
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