So I've been doing some looking around and I've understood the first O2 (upstream) is for A/F and the second O2 (downstream) is essentially for checking if the coverter is working. I've been having a problem with really bad LTFT like down in the -20/-30 percentiles and my car was recently up at...

Repectfully request advice: Low O2S2 voltage & high LTFT caused by bad Catalytic Con vehicle: 2011 Cruze LT 1.4L turbo, 67K miles (This car was not properly maintained by the previous owner.) Long Term fuel trim ~ 12.7 O2S2 (down stream O2 sensor) voltage .67 vacuum at idle after warm up ~...

Alright, so recently I started using the Torque app. I've noticed that I'm running -8% LTFT, which is quite concerning. The only mod that I have is a K&N RAI. Just today, I had a MIL pop. I forget the code, however it was for slow switching of my B1S1 O2. What I'm hoping is that the negative...