2012 gmc acadia code 0420

The thing is it sounded like the mechanic already diagnosed it as a bad cat but said it wasn’t worth it to fix it. Thus the question. $150-300 on a 2012 seems like a reasonable repair and I’d either do it myself or find another shop that values fixing cars.

The OP is taking it to a different mechanic.

Ah I see now said the blind man. Missed that post.