My check engine light was on, and returned a code of P1135 - Air/Fuel Ratio Sensor Malfunction. There was a hole in the flex pipe, so we changed out that one exhaust piece (down pipe, flex pipe, catalytic converter) But the code still pops up. I had to take it to the shop to get it inspected, and the guy at the shop(who I don't trust) says he wants to run diagnostics on the sensors, the circuitry, the computer, and to check for vacuum leaks. The car runs great, and I want to spend as little money as possible to fix this problem. But my car won't pass emissions inspection with the check engine light on related to a emissions sensor issue... My friend told me that it is most likely the O2 sensor after the converter, and that I should just change that out... But its like $140, and I have no idea if that is likely to be the problem or not... I don't want to give any more money than absoultely necessary to the shop guy, I only want to bring it back there to conclude my inspection...Anyone out there who knows what the most common problem would be in this situation that could help me out? I would greatly appreciate it!!!!