P0420= catalyst low efficiency, this means it's probably time for a new cat and O2 sensors, 160,000 is over the useful 100,000 miles on the O2's, check the cat for melted or broken up bed, this could be the cause of your rattles, pieces of the cat are stuck in your muffler or pipes, you may need to replace the entire system cat and all!
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Friday, August 20th, 2010 AT 8:54 AM