B & M Muffler

In July 2010 I brought my 2003 Buick Century in to B & M Muffler in Tolleson, AZ for replacement of a catalytic converter. The shop charged me about $300. They also cleared a P0420 trouble code which is "Catalyst System Efficiency Below Threshold". A few months later, the P0420 code returned and I called B & M. The engine codes were cleared again and I was told to complete another "drive cycle" to reset the system. After a couple more months the check engine light came on again. The codes were cleared again and I replaced both oxygen sensors. After a couple more months, the light returned. I was getting tires at [redacted]s at the time and asked them to diagnose the P0420 code. They told me it was due to an improper catalytic converter (universal fit, not direct fit) installed on my car. I brought the car back to B & M and told them to diagnose the P0420 code and they told me it was because of leaking intake manifold gaskets and carbon buildup in the intake system. I had them perform the work with the understanding this would cure the trouble code problem. This work was about $1,000 Again, the system was reset. A week later the P0420 code came back so I returned to B & M. Their diagnoses showed an inefficient catalytic converter so they replaced it and gave me partial credit for the old one but I still paid $140. Again the code was reset. A month later the P0420 code was back. I returned to B & M and this time they stated they had overlooked my car required a California compliant converter. They replaced it for free this time. A year and a half later the P0420 code was back again. This time I paid [redacted], who regularly services my car to diagnose it. They told me the universal fit catalytic converter was the problem. I took it back to B & M and had them diagnose the P0420 code. They told me the O2 sensors I had replaced less then two years ago were bad and this was causing the trouble code. I paid them another $220 dollars to replace them and the system was reset again. Two weeks later the P0420 code was back. I returned to B & M and this time they said the code was caused by a water pump that was starting to show signs of leaking. The car has never given any indication of overheating and this reason was not indicated in B & M's diagnoses which replaced the O2 sensors. It appears to me B & M is just making excuses to cover for an inadequate converter.