My check engine light keeps coming back on with the code P0420 on my 2015 Chevy Cruze LT. I've replaced the front catalytic converter, both O2 sensors (one is aftermarket and one is GM made based on advice from a Chevy mechanic), replaced all the spark plugs, replaced coolant hoses, the coolant container, did a smoke test and found no leaks... I'm out of ideas on how to fix this code. The car drives just fine unless I ride it hard (fast accelerations and/or high speeds for long distances), then it will stutter and the check engine light will flash. If I back off and give it a few moments, the…
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