Okay, my check engine light is on as the title says. at first it would go on and off, usually on when i first started up the car then off the rest of the day. this happened here and there. but now it stays on. at first we thought the re-flash was the problem but that wouldnt explain the randomness of the light, because software does not just go "hey i think i will screw up for only 1 hour then be fine". once software is corrupted its corrupted so we threw that idea out. we did a system check and got codes thrown back at us for both O2 sensors. now this seems simple enough, bad O2 sensors happen here and ther when the exhaust gets changed, for whatever reason. but i dont want to go get new O2 sensors if its not the real problem. i also believe that maybe the cat is going because its staying hot way longer than it should afterthe engine is cooled down. now if its the cat, that might explain why the computer throws codes for the O2 senors because they are both hooked right into the cat. does anyone know how i can check these things without completely tearing things apart or buying parts i dont need?

 

get a friend with the same car and swap O2 sensors to check it, swap the cat if thats not it. does the car run differently(bogs easier then it used to, or gets warmer then it used to ,or over heats), smells like rotten eggs(often from the cat being bad), or excessive smoke from the exhaust?

 

first obvious reason could be u didn't tighten the gas cap.

anything beyond that, it could be any of 100 problems. a light is just a light. it shows something is wrong. the only reason to know what went wrong is to get the error code read using a OBDII scanner.

 

lol, definetly not the gas cap. i have a feeling its the cat. absolutely everything else is prestine, tight and so forth. the car actually runs really well, but yes i do notice the rotten egg smell, and thats one of the other reasons i believed it was the cat.

 

well go get the code scanned. it could be something as harmless as cat not doing its job (the egg smell is normal though. it's not a malfunction) or something as serious as cylinder misfire or some sensor not responding.

 

You can either goto Autozone and have them check it, or goto this page and it'll tell you how to do it yourself.
http://home.comcast.net/~rsxmachine/info/CEL/

 

luckely i do have a scanner and it always throws the same two codes, one code is for the upstream O2 sensor, and the other code is the downstream O2 sensor. yes, it would seem obvious that it would be the O2 sensors and thats all, but like i said there was a few other things i think that would lead me to believe its somthing else. back to what i said about the re-flash. i figured if the software is corrupt or just programmed badly possibly TO MUCH fuel is being pumped in and thrown out through the manifold (header) which would still cause the O2 sensors to possibly freak but also the car to malfunction. i know someone with an 02 si so im going to try to get them down to the garage and do some swappin until i figure it out. if it is the ecu hopfully when i send it back to get the k-pro upgrade it will be fixed. now if i can find a stock ECU to plug in for just inspection so i can pass , lol. damn "off road use only" crap!

 

have you checked the fuses? recently happened to my friend's evo, due to short circuit.