reseting the engine check light

[Where's my car?]

So here is the thing. I ended up spending another 250 dollars getting my car fully checked for the problem. The guy told me that of the two codes p1128 and p1130 there was a total of seven possible faults. He said after checking the faults which included the MAF, Oxygen Sensors, the Manifold, Oil Pressure ect.... He came to conclusion that my Custom Magnaflow Exhaust was causing some sort of back pressure that the car was not use to therefore causing the engine check light to turn on. CAn this really happen. I only swapped out the 3 inch in length piping after the 4 cats and the mufflers and the tips. NO change in between cats and headers. Can anyone give me some advice, or anything.