I have a 96 Yukon. Dropped a crate motor in September.

Last month I had a Magnaflow Performance Exhaust 12588 Stainless Steel Muffler with 3 inch inlet/Outlets installed with new 3 inch tailpipe.

Today I decided to replace the rest of the exhaust set up from manifold to the Muffler. I had 2 left over hi flow Magnaflow 59926 Metallic-Cat Universal Spun Metallic Catalytic Converters that I didn't use on my Mustang so I thought they would be useful. So I took the truck to Meineke and had them pull the old pipes and the old cats and redo everything from manifold flange to the muffler.

Between muffler and cats I have 3 inch pipe. between the exhaust manifold to the cats inlets I have 2 1/2 inch pipe. They installed the O2 bungs in the exact places they are supposed to be and all 4 O2's are brand new. There was no CE condition prior to today.

The truck runs awesome. It opened up a lot. Sounds throaty too. I drove on the parkway for about 5 miles, then while I was driving locally the check engine came on. I don't have a scanner to pull the code tonight but I'm wondering if the universal hi-flow cats messed with the reading the O2 needs or is it the larger pipes diluting the reading?

Ill get my son to scan it tomorrow to see the exact code.