Check engine light after muffler work new information

TexasGopher · July 30, 2022

I have a 2013 GMC with 150K on it and recently installed a one in two out muffler. After a couple of hundred miles it's now throwing P0172 and P0175 codes, rich bank one and two. Is this an O2 sensor problem or is there something else going on?

I'm not happy with the work the shop did but there isn't much I can do about that now. They put some very short mufflers on it and it was way too loud. Their solution was to put a resonator between the cat and the muffler. It's still too loud for my taste but that is between me and the shop.

Is there a problem with the installation or did it bork the O2 sensor or is there another issue here. It wasn't throwing code before this was done.

Edited August 22, 2022 by TexasGopher

CamGTP · July 31, 2022

Maybe it's plausible that welding on the exhaust did something to the sensors but it's really tough to say.

A scan tool that can watch fuel trim should be used to see what is going on.

dna9656 · July 31, 2022

Any increase in flow capability (your 1 input into 2 outlets) is wasted effort and money. If ANY section of the exhaust is smaller than the largest passage in the exhaust path the most flow you can get is the flow of the smallest passage.

TexasGopher · August 1, 2022

I wasn't looking for a performance gain, just a change in exhaust sound. I went a little overboard and now this.

TexasGopher · August 22, 2022

The shop that did the original work has apparently closed. The Flowmaster he put on it was just too fricken loud. I had another shop put a Borla muffler on and it sounds much better. They told me the first shop cut out the third cat when they did their work. did that third cat have an O2 sensor and could that be causing the check engine light?

I cleared the code after having the new muffler installed and drove it almost 300 highway miles but it came back on about 10 miles after a fill up.

At this point I'm just trying to get some ideas of what is going on before I put it in the shop.

Looks like another case of beware of the fly by night shop.

KARNUT · August 23, 2022

32 minutes ago, TexasGopher said:

The shop that did the original work has apparently closed. The Flowmaster he put on it was just too fricken loud. I had another shop put a Borla muffler on and it sounds much better. They told me the first shop cut out the third cat when they did their work. did that third cat have an O2 sensor and could that be causing the check engine light?

I cleared the code after having the new muffler installed and drove it almost 300 highway miles but it came back on about 10 miles after a fill up.

At this point I'm just trying to get some ideas of what is going on before I put it in the shop.

Looks like another case of beware of the fly by night shop.

On my 14 I did a muffler delete and left the cats on. It wasn’t that loud at all. All the sudden after 40 years plus driving I wanted less sound. I put a mega flow on. You only heard it when getting down on it. Never a code. The 14-15 model years many people cut off the 3rd cat no codes. The exhaust stock is pretty high flow. Something else seems to be going on changing mufflers and removing the 3rd cat was common and posted on this website during those years, without problems.