O2 Sims - Few questions
Thread Starter
Racer
Joined: Aug 2005
Posts: 307
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From: Bay Area CA
O2 Sims - Few questions
So I got a CEL today, I found the code to be P0420 which is basically saying the difference in oxygen readings being reported by the front O2 sensors isn't different enough from those being reported by the rear O2's. In other words my cat isn't doing as good a job as my PCM would like to see. This makes sense beause I just installed Dynatech LT's with high flow cats.
I cleared the code and for now all is good. I did a little searching through the forums and found either getting the rear O2's programmed out or installing O2 simulators would correct my problem. I'll probably just get the O2 sims but I dont know exactly what they do. Will they cause me to fail smog? Basically what do they do and how will they effect my car.
On a side note I'll probalby be adding two more high flow cats for the sake of passing the sniffer when the time comes. Assuming the car is cleaner after adding the additional cats I probably wouldn't throw this code again correct?
I cleared the code and for now all is good. I did a little searching through the forums and found either getting the rear O2's programmed out or installing O2 simulators would correct my problem. I'll probably just get the O2 sims but I dont know exactly what they do. Will they cause me to fail smog? Basically what do they do and how will they effect my car.
On a side note I'll probalby be adding two more high flow cats for the sake of passing the sniffer when the time comes. Assuming the car is cleaner after adding the additional cats I probably wouldn't throw this code again correct?
Race Director
Joined: Oct 2002
Posts: 16,477
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From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
02 sims are small electrical modules that plug into the wiring harnesses now connected to your rear (after-cat) 02 sensors.
Their function is to provide a fluctuating voltage signal which replicates the signal the 02 sensors would produce with functioning cats. They were designed for the people who run no cats at all, to not throw any codes.
Most who have to endure only an OBDII computer smog test will pass no problem with them. Simply put, with this sort of test, if the car isn't throwing codes, you pass.
With you being in Cali, your luck might not be so good. You should be able to pass the computer and sniffer tests fine with the hi-flow cats (and the sims), but getting by the visual inspection might be a different story.
Their function is to provide a fluctuating voltage signal which replicates the signal the 02 sensors would produce with functioning cats. They were designed for the people who run no cats at all, to not throw any codes.
Most who have to endure only an OBDII computer smog test will pass no problem with them. Simply put, with this sort of test, if the car isn't throwing codes, you pass.
With you being in Cali, your luck might not be so good. You should be able to pass the computer and sniffer tests fine with the hi-flow cats (and the sims), but getting by the visual inspection might be a different story.
Drifting
Joined: Oct 2003
Posts: 1,540
Likes: 0
From: bloomfield nj
simms simulate the rear o2's.they create the happy voltage changes to keep the pcm happy[they work just like the o2's].rear o2's have no influence over mixture.they will not set a faults and the pcm will run the i/m for it and pass. your cats are right behind the collectors aren't they?if they are right at the collectors they will get enough heat to fire off quicky and if you still have seondary air tthat will also help fire them off. why would you want 4 cats?f that's the case you were better off leaving it stock.if you haven't had it tuned there is a chance you will be on the fat side usually headers and cold air packages set the fuel trims to the mid/high +'s.
Thread Starter
Racer
Joined: Aug 2005
Posts: 307
Likes: 0
From: Bay Area CA
Thanks for the replies guys.
I had read from forum members that passing the sniffer wouldn't be a problem with these LT's and high flow cats but after getting this CEL I'm a little skeptical. If the code being thrown is telling me that my cat isn't doing as well as it should then wouldn't I be less likely to pass smog?
I probably should get a tune, I'm holding off right now because I may end up changing everything back and I don't want to spend a few hundred dollars for nothing. The only reason I would change everything back to stock would be fear of being busted by the Man. However if I can find a Corvette friendly smog shop that may look the other way on the visual then I would like to keep the system and then add two more cats. Adding additional cats would not only make passing the sniffer more likely but I would also be running the same number of cats (4) that my car came with in stock trim. If it weren't for the wonderful state of California I probably wouldn't be running any cats at all.
I had read from forum members that passing the sniffer wouldn't be a problem with these LT's and high flow cats but after getting this CEL I'm a little skeptical. If the code being thrown is telling me that my cat isn't doing as well as it should then wouldn't I be less likely to pass smog?
I probably should get a tune, I'm holding off right now because I may end up changing everything back and I don't want to spend a few hundred dollars for nothing. The only reason I would change everything back to stock would be fear of being busted by the Man. However if I can find a Corvette friendly smog shop that may look the other way on the visual then I would like to keep the system and then add two more cats. Adding additional cats would not only make passing the sniffer more likely but I would also be running the same number of cats (4) that my car came with in stock trim. If it weren't for the wonderful state of California I probably wouldn't be running any cats at all.
Melting Slicks
Joined: Mar 2003
Posts: 2,744
Likes: 9
From: FL
Cruise-In VI Veteran
Even if the car is running perfectly... you may see rear O2 codes.. Just due to the heater circuit and "insufficient switching" of the sensors. Must tuners will disable them or change the mode of the code, so it wont set a light even with cats..
My Camaro SS did the same thing, had highflow cats and all.. Still set rear O2 codes..
My Camaro SS did the same thing, had highflow cats and all.. Still set rear O2 codes..
