Malibu V6

• Automatic transmission
• 91,000 miles

Replacing the catalytic converter with a "Universal converter" that is welded in line would have been enough for most models, but not the Malibu. After a week passed, the "Check Engine" turned on. A local shop reported a code P420, "cat. convert. not working efficiently:. After talking to two muffle shops the "Universal converter" will work sometimes, unless the Check Engine light comes one and then must the Universal must be replaced with the OEM version. One muffler shop indicated they had a Universal-HM for heavy metal(not a rock band) that would work and the Check Engine code P0420 would not come up. Of course, asking the Chevrolet dealership, they don't know what the problem is. They only handle the OEM version of the cat. conv. and can't speak about the Universal converters.
In one of the blogs there was information about GM replacing cats that were poorly made and broke apart prematurely and caused rattling in the converter eventually plugging up the exhaust system causing no or low acceleration with low engine performance. Guess what, GM doesn't cover Malibu's. They only cover the models with the 3.4 and 3.8L engines. Sounds like there's more coming your way GM.
Am I paranoid about this POS GM car? First intake manifold gasket repair, then AC control module repair, then Anti-Theft module reset and now the cat conundrum.