After head gasket, P0401, Catlyst, and O2 Snsr.

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Had head gasket replaced by ASE certified master mechanic, now engine codes are P0401 (insufficient egr flow), Catlyst, and O2 Snsr. I didn't notice any smoke when the gasket blew, but now, even after the repair, the car has hardly any power. The car is my wife's 2002 Honda Civic EX 1.7 Auto 4DR. Any qualified help is GREATLY appreciated.