CEL for P0159 and P0158. How to fix!?
 

As per AutoZone references:
P0159 - Sensor circuit slow response ( Bank 2 Sensor 2)
P0158 - Sensor circuit high voltage ( Bank 2 Sensor 2 )

so now what..i was told this might be the O2 sensor since i had put in a HKS sport exhaust ... and yes the Cat is still on it. Also should i wait for the CEL to pop up again before i take action. Code had been deleted by AutoZone. Please advise thanks.

a catback should nothing to do with this code. your code is for a secondary o2 sensor which your 2k1 cali spec car has two of. both are before the main cat so unless someone was just really careless then you just have a bad o2 sensor. if it is truly bad then the code will cycle back out.

First thing to do would be to look at the threads that already cover this topic.

i had they same code and i replace my o2 sensor , then the problem was gone.

thanks ... how much would it be to replace the 02 sensor? any highly recommended?

check them out at www.oxygensensors.com they had the best prices last time i replaced one.