I had them replace the catalytic converters on my car in September 2012 and within a few weeks, the check engine light started coming on. I had it checked out a couple of times and the reading kept coming back saying there was a problem with the catalytic converters. I took my car back to them and they said there was something wrong with my car that was causing the converters to fail and I needed to take it to a mechanic to figure out what was wrong. I took my car to a very reputable automotive shop and after extensive testing, they determined the problem was the front converter was not the right one for my vehicle. I took my car back to Mighty Muffler, along with a detailed explanation of the problem from the mechanic and a letter from the Colorado Department of Health & Environment explaining problems with improper after market converters. Even with all that information and a 1-year guarantee from them, they refused to fix the problem. They insisted they installed the right converter, the mechanic didn't know what he was talking about and there must be something else wrong with my car. I now have to pay an additional $400 to get the proper converter installed so that the car will pass an emission test and I can get my license plates. BEWARE - there is a reason they can offer the lowest price on converters!!!