Finally was able to get my codes scanned today. Here they are.

P0420- catalyst system efficiency below threshold-bank 1
P0138- Bank 1 Sensor 2 Circuit High Voltage
P0139- Bank 1 Sensor 2 Circuit slow to respond

I know I have a leak in my J Pipe but Im sure that is completely unrelated. These codes are intermittent. The come and go as they please. Some times they stay on for days, sometimes only for minutes.

Nothing seems to be too out of the ordinary for the car. She starts a couple cranks slower now and my mileage dropped from 28-30 on the MID to 26. I am going to try to replace the O2 sensor on Friday but don't want to install it if it is something else. I read the P0420 is a bad pre cat code. I have a set of High Flows waiting to go on but I haven't had the time. Thanks for the help

 

I wouldn't be surprised if the sensor connection got screwed up/knocked loose when the J-pipe went on.... Maybe even the leak burned the connection (can't really picture proximity of j-pipe to the sensor wiring right now). That's where I'd start....

 

has any fuel injector cleaner, seafoam, fuel treatment been added lately? ive seen those codes on after a fuel injection service.

 

Yes I seafoamed the car but that was after the codes started showing up. Im going to try to install my Hi Flow Precats, HFC, and new 02 sensor on Thursday.

 

I could see a leak in the j pipe causing that... Bank 1 sensor 2 is the downstream o2 sensor I assume. If your leak is before the o2 sensor, it could cause o2 sensor faults. It's not gonna read what is actually coming out of your catalytic converter but instead a mixture of outside air and cat-treated exhaust fume.

 

I replace the O2 sensor and haven't seen a code yet. Ill be doing a custom true dual exhaust in the near future doing away with the J Pipe

 

I have a similar problem that I have gotten some advice on but still no solution. I installed RV6 pre-cat deletes on my 05 TL on both banks with secondary O2 sensor spacers. Now I have P0139 and P0159 code. I started with the cat deletes so the rest of my exhaust is factory. Cleared faults but they keep coming back. Not sure what the problem is??

 

Since I replaced my sensor I haven't seen a code. I can't be much help but my guess is you need adownstream sensor on each bank. Did you install your O2 sensor spacers upstream or downstream

 

They are definitely downstream, I hope the sensors arent bad...... It does sound like I have a exhaust leak, kind of a pinging rattling noise at idle. Im thinking that might have something to do with it