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Discussion Starter · #1 ·
Hey guys,

Looking for some advice. I purchased a 2002 gts years ago. I have to smog for my state emissions test. The heated o2 sensor reads incomplete. The rear oxygen sensors were replaced with dummy sensors by a previous owner. So no issues with check engine lights etc. today I replaced the rear dummies for correct o2 sensors. I guess my question is, why would someone replace the rear sensors with fakes? I’m hoping after I drive it tomorrow I’ll be ok but I’m almost certain that won’t be the case. Please advise if at all possible. Thank you all very much.


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If the cats were removed fake sensors would be used to fool the computer into not throwing a code. Does your Viper have cats?
 

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Discussion Starter · #3 ·
Yes it does. idk if the previous owner had removed them at some point etc.



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Probably has a tune?

If you have the sct supplied with the car, set the tune back to stock drive a few times it will pass.
 

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Discussion Starter · #5 ·
I don’t have a tuner with it. If it was tuned, how can I set to stock now?


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Could it also be bad O2 sensors?
 

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I believe only the fronts are heated, not the rears. A lot of folks have had problems with non-OEM front O2s. Do not toss your rear sims, you can't get them anymore.

If your car has sat for a while, or only gets used for short trips, then your PCM may need a couple of 20-30 minute drives at steady cruise rpm with the A/C on to update the fuel trims.
 

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Discussion Starter · #9 ·
They get Very hot. I’m trying to complete a drive cycle. If that monitor remains incomplete I will remove the exhaust and confirm


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If you have or can borrow a temp gun, it would tell you if both cats are heating up in unison. You could have plugging issues on one side that is leading to O2 problems. Cats normally operate in the 600F range and vary according to whether they are oxidizing or reducing the exhaust flow.
 

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Discussion Starter · #11 ·
All emissions tests passed this morning. Thank you all for your helpful info. Thankfully the downstream o2 sensors fixed it. I really appreciate all of you and this forum


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