i'm workin on a 94' st celica atm, and it has 2 02 sensors, one in the header and one later in the flex pipe. We're putting on an aftermarket E-bay header and flex pipe, and the header itself has a spot for the first O2 sensor, but there is no hole for the secondary O2 sensor in the flex pipe. What am I to do? will the car run correctly w/ just the primary O2 sensor connected.....is there any kind of trick to get this set-up running correctly. any help would be apprechiated, we're tryin to get this car on the road at the moment

yep I had that problem too..

but I found that just plugging the 2nd 02 sensor (or not even using it) will not cause a CEL

so I only have the 1st 02 plugged in.

thanks alot daniel ... just runnin the first o2 sensor as well, and it seems to be doing fine

would it still run the same if u only had the 2nd o2 sensor plugged in?

well i get a check engine light everytime i have the AC on and under heavy acceleration.. i usually just clear it and ignore.. I want to weld the 2nd O2 sensor behind the cat under my car to see if that helps..

does anyone know if a CEL code only gets pulled once, if several successful starts will automatically clear it? My friend was saying something after 7 starts or like 100 miles or something... anything like that true?

well I pulled the code today, # 27  Sub-Oxygen  ON  ON  Sub-Oxygen Sensor Or 
  Sensor    Circuit, ECM 
  Signal

This post has been edited by Jaws4God: Oct 17, 2009 - 4:34 PM

Alright, so you plugged the 2nd O2 Sensor up and it worked? What did you do with the second O2 sensor? I have both screwed into my ebay header (I know, it sounds stupid) and I do have a CEL. What you did sounds very good to me, but how did you get rid of the second O2 sensor?

I tried to have my 2nd one relocated to the cat as well but no one would touch it.

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yeah i tried having the 2nd O2 sensor right below the first one on the ebay header and it had the CEL on all time.. so right now the 2nd one is just plugged and only throws the CEL if I do heavy acceleration.

I am going to get a 2nd O2 sensor and weld it behind the cat thats under the car. I already bought a nut for it and will have a friend weld it on.. Problem is I bought one of those cheap universal ones and my friend won't touch it.. he said i have to buy OEM which is like $150

Autozone sells a bosch one for 109 bucks. I couldn't find a mech to extend the wire so it would reach the cat. What about you, I mean how are you going to get the wire extended? Sounds risky if a mech won't do it.

get a 2nd bung welded then google the "spark plug non-fouler trick" and you'll be all set with no check engine light when you connect and install that sensor.

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I already have both O2 sensors plugged into the header at the same location (I know, sounds stupid). So all I have to do is get this spark-plug non fouler set up to work and that's it? Just out of curiosity...what if the check engine light is still on?

...Alright, I googled it and read a rather long post about it and it seems to me that there could be some risks (correct me if I am wrong) with this set up. What exactly are those risks? Would canceling out the second O2 sensor via the mod, potentially cause running either leaner or richer? The thread starter, 'Aaron', mentioned detonation too and that kind of scares me a bit.

This post has been edited by 6G96GT: Oct 18, 2009 - 10:15 AM

the purpose of the 2nd sensor is to verify that the warmup cat is there and working. it does not affect the fuel trims of a/f ratio.