Rear o2 sensor necessary with no/high flow cat?
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This is a discussion on Rear o2 sensor necessary with no/high flow cat? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I am curious, if you have a high flow or catless downpipe, do you need to bother with a rear ...

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    Rear o2 sensor necessary with no/high flow cat?

    I am curious, if you have a high flow or catless downpipe, do you need to bother with a rear o2 sensor? My understanding is that the front O2 sensor is responsible for fuel mixture, and the rear O2 sensor is responsible for emissions. That being said, if you don't have a cat, you aren't going to meet factory specs for your rear O2 sensor. So, is it even necessary?

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    Registered User Rexxy2Sexxy's Avatar
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    Bumping this thread i have the same question

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    Registered User SRTSamb's Avatar
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    Quote Originally Posted by pfcrangel View Post
    I am curious, if you have a high flow or catless downpipe, do you need to bother with a rear o2 sensor? My understanding is that the front O2 sensor is responsible for fuel mixture, and the rear O2 sensor is responsible for emissions. That being said, if you don't have a cat, you aren't going to meet factory specs for your rear O2 sensor. So, is it even necessary?
    Eric at TP says you do. I had a similar question earlier
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    Master Baiter EJ257's Avatar
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    32-bit ECUs require the rear O2

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    Registered User Rexxy2Sexxy's Avatar
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    k thank you!

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    Moderator Donkey's Avatar
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    Just to add on to what Matthew said,unless you totally defeat the rear 02 codes for the 16 bit you will fail emissions.
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    Registered User Rexxy2Sexxy's Avatar
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    I was just worried my sensor was shot.. but its golden surprisingly

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    Registered User kjgreen33's Avatar
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    If you live in Colorado where they don't do emissions testing.....it would be unnecessary then?

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    Moderator Donkey's Avatar
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    Quote Originally Posted by kjgreen33 View Post
    If you live in Colorado where they don't do emissions testing.....it would be unnecessary then?
    Depends on what vehicle you have. If it's an 02-05 WRX then you can ditch it.
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