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P0420 maybe o2 sensor?

Old 07-15-2015, 03:54 PM
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P0420 maybe o2 sensor?

So i replaced my rear o2 sensor a while back and ever since then i had a p0420 code but the thing is i think i put a front o2 on the rear (it has a really long wire) i ordered it on rock auto some generic one there wasnt even one in the car before and all i got was a low voltage for rear 02 cel which is understandable so i dont know if its because the cats bad the rear o2 is potentially a front one (if even possible) its because its generic or my cats bad (unknown aftermarket cat) anyone have any ideas?
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Old 07-15-2015, 03:57 PM
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P0420 is Catalytic Converter Below Efficiency Threshhold. I haven't seen a single case where it wasn't a blown out or gutted cat. The fact that there was no rear O2 also highly suggests that the cat is gutted.

The rear O2 can be a cheap generic O2 without any problem (it can also be missing without a problem other than a CEL), it's the front O2 that is much more expensive (~$250) and not something you can go generic on at all.

Pull the cat and look inside the front. I bet it's gutted:
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Old 07-15-2015, 04:10 PM
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Originally Posted by RIWWP View Post
P0420 is Catalytic Converter Below Efficiency Threshhold. I haven't seen a single case where it wasn't a blown out or gutted cat. The fact that there was no rear O2 also highly suggests that the cat is gutted.

The rear O2 can be a cheap generic O2 without any problem (it can also be missing without a problem other than a CEL), it's the front O2 that is much more expensive (~$250) and not something you can go generic on at all.

Pull the cat and look inside the front. I bet it's gutted:
Guess i dont have any choice but to try and take off those stubborn bolts haha was hoping maybe its something else but thats what everythings pointing to i tried to take it down before and none of the bolts would even move hit them with looseners and more torque nothing haha
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Old 07-15-2015, 04:17 PM
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You are dealing with the splines. This is what the front cat bolts look like:


No amount of torque will get them to rotate, the splines are locking it's position. Once you have the nuts off the back, hammer them out with a hand-sledge. Replace them with M10 exhaust bolts and nuts from your local auto parts store.
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Old 08-13-2016, 06:17 PM
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Hey guys,

So I just popped the p0420 after about 500 mIles with the bhr midpipe. I was under the impression that the midpipe was made in a way that it wouldn't pop CAT lights. Is it possible that my o2 sensor is fouled, or is it just a midpipe thing? Thanks, sorry if this is something that has been killed a dozen times. I just speny a half hour in search and nothing turned up that was specific to my problem.
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Old 08-13-2016, 06:26 PM
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Yes, it's normal.
I have one. I use the Torque app for Android to clear it when it pops up.
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Old 08-13-2016, 06:30 PM
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Awesome, thanks!
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