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post #1 of 6 (permalink) Old 06-21-2013, 06:22 PM Thread Starter
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Mpg O2 Sensor.

Sorry to make another thread on this, but just a quick question. If my o2 sensor is causing mpg issues, would it be the upstream or downstream one? (or could be either?)

As I refereed on my other thread, I have a few other things I'm looking at, but just trying to get more details on that one particular "could-be"

Thanks!

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post #2 of 6 (permalink) Old 06-21-2013, 07:17 PM
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If you have a bad HO2 sensor it will set a code telling you which one is bad.

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post #3 of 6 (permalink) Old 06-21-2013, 07:24 PM Thread Starter
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Quote:
Originally Posted by Coby7 View Post
If you have a bad HO2 sensor it will set a code telling you which one is bad.
I was told, which could be untrue, that just because an o2 sensor is off causing bad fuel usage, it may not necessarily be "bad" enough to throw a code...yet.

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post #4 of 6 (permalink) Old 06-22-2013, 05:14 AM
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yup that's true, once it gets past a certain value range the pcm will set off the light.

My rear o2 died and dropped me about 7mpg's. When my front screwed up I honestly didn't pay much attention since the light illuminated on my way to work and it was fixed the same day after work, but normally the upstream kills mpg in most vehicles.

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post #5 of 6 (permalink) Old 06-22-2013, 06:09 AM
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Either HO codes will make "PCM" or "ECM" go to a preset value matrix always causing your car to be harder on fuel.

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post #6 of 6 (permalink) Old 06-22-2013, 07:00 AM Thread Starter
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Quote:
Originally Posted by money_man View Post
yup that's true, once it gets past a certain value range the pcm will set off the light.

My rear o2 died and dropped me about 7mpg's. When my front screwed up I honestly didn't pay much attention since the light illuminated on my way to work and it was fixed the same day after work, but normally the upstream kills mpg in most vehicles.
That would be the hard to get to one in the header wouldn't it. :(

poo

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