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Re:Normal voltage on a rear H02S

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06 Jan 2021 15:39 #45742 by Tek24
Normal voltage on a rear H02S was created by Tek24
Hello, just went through chapter 4 and idk if I missed it or not but what should a normal working oxygen sensor after the cat look like voltage wise? From what I understand about how the cat works you should see voltage near .700 to .800mv because there’s less oxygen after the cat. Is this correct? If anybody could help I’d appreciate it.

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06 Jan 2021 20:39 - 06 Jan 2021 20:40 #45747 by Tutti57
Replied by Tutti57 on topic Re:Normal voltage on a rear H02S
Around 750mV is normal once it's warmed up at idle. If you lean or richen the mixture they will respond, but there should be a delay before you see changes, unlike the instant change you see from the front sensor(s).



Nissan Tech
Last edit: 06 Jan 2021 20:40 by Tutti57.

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06 Jan 2021 21:55 #45750 by Tek24
Replied by Tek24 on topic Re:Normal voltage on a rear H02S
Thanks for the respond. One other question I had related to this, in the video on YouTube where Paul was working on a Isuzu Rodeo with the reversed upstream sensors, at around 16:33 he mentions briefly while looking at the rear O2s that bank 2 has a better working cat than bank 1, but from what I can tell bank 2 is running lean, wouldn’t a cat that has the higher voltage be the better working cat? I’ll attach the video in question.

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09 Jan 2021 09:44 #45793 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Normal voltage on a rear H02S
An O2 sensor is a fuel cell it isn't really an oxygen sensor some people call it the tomato sensor the normal Lambda sensor only really produces voltages very close to 0.9v or 0.1 volts nothing in between.

If the cat is burning all the combustable fuel products in the exhaust and leaving only a very tiny amount of oxygen it will flat line around 0.1v

If the cat is burning all the available oxygen but a even a tiny ammount of fuel is left it will read close to 0.9v

If the engine is is running in closed loop and the fueling is controlled close to stoichiometric by the upstream O2 it could show either --- normally on cars I expect see 0.1v at idle.

If with the engine warm at idle you see the downstream sensor following the up down peaks of the upstream sensor the cat is not working.
For asscessing how efficient a cat is at doing its job you have to do an reserve oxygen storage test --- Paul has acouple of good premiium videos on this and covers it in section 5 of the book

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



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11 Jan 2021 10:36 #45837 by Tutti57
Replied by Tutti57 on topic Re:Normal voltage on a rear H02S
Remember that the sensor has to be warmed up to produce voltage too. Some manufactures (like Nissan) will show a preset value until then. I saw 1.75v on two rear sensors the other day until they were warmed up, and that was normal.



Nissan Tech

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18 Jan 2021 08:03 #46006 by Tek24
Replied by Tek24 on topic Re:Normal voltage on a rear H02S
Thank you guys, for helping with this, I’ll have to check out those videos

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