So I've been having cold start problems for a while where my car would die or run really rough until it warmed up. Well I was throwing the bank 1 sensor 2 no activity code. I was running a catless dp and a trifecta tune. What I thought was somehow the tune didn't erase the code for the catless dp and thats what I was getting but after putting the cats back on and going to the dealer and having it cleared I've still got the code so the sensor must actually be bad but my question is can the downstream sensor be the cause of the problems? I know in the LS1 world with headers you delete the rear 02s and tune the codes out and it'll run fine so wouldn't it be the same for the Balt? With a bad rear 02 wouldn't my only problem be a CEL? thanks

 

what downpipe do u got? most of the ones made have the o2 bung at an angle out of the exhaust stream so there is no code regardless if u have it erased from the tune or not. sounds like ur o2 sensors are bad, iv has both go, and yes the second one does throw codes when its bad but iv never had it run bad when my o2 sensors were bad. maybe some others could input. did u have a tune before u got ur downpipe, i found that on tune with stock downpipe it killed my primary o2 cause of the heat the cats generated on full boost i guess, as soon as i got catless, no more issues

 

My first mod was a k and n intake and then the catless downpipe followed by a trifecta. It ran fine for a while but when it started getting cold the running rough on start up started. I've got the modern performance dp with the angled bung. It also had a lean code at the dealership. Once they cleared it and I left it didn't make it 20 minutes before I got the bank 1 sensor 2 code again.

 

Mine also did that cold start problem, no CEL though, the rear O2 sensor code is deleted.
As soon as ive put the stock downpipe back on it solved the problem.

I was also tuned for the downpipe... the only thing is the rear O2 sensor was not in the bung, with the badmab the wire get squeezed a little on the chassis i did not wanted to damage it, i just wrapped it in aluminium foil and zip-tied it on the heatshield near the downpipe...

I dont know if that was my issue, but i have no problem since i installed the stock downpipe.
Vince said everything seemed perfect on the tune, it was running erratic for 3-5 seconds then it was fine.

 

When I put my catted dp back on it might have helped slightly but it didn't cure it by no means. A friend of mine is the manager over another dealership and he said it could be oil from the k and n on the maf. But thats what I don't understand my car is tuned for a catless dp so the code should be deleted anyway. How is it coming on?