2001 Gmc Sonoma Replaced Cat Last Year Rear O2 Sensor Check Engine Light Came

i bet you used an aftermarket cheap cat converter. thats what happens with the aftermarkets. i refuse to use them as they do not contain enough precious metals to last. you need another one. see if they will warranty it for you and if they do be prepared for this again. otherwise, do it right and get a factory cat which will be more money

Roy