check ur engine dianogsis, this happened to me once..its not the O2 sensor that spoilt but the ecu itself...
no more error code once new ecu plugged..
wish u luck...
check ur wiring of the pen timer too......for blktop.....u need to connect the timer ground to ecu ground......do not ground it to any part of the body...silvertop if diffrent....last time my 20v blktop 02 koyak no error code.....