ok so i take my 4runner wgich is regitered as non op, to be smoged so i can register it n get it tagged. since it was a non op, i used the battery for my sisters car but i put it back into the runner to get it smogged. it didnt pass because of disconnection of the battery so the tech told me to drive 25 miles n to come back for the free retake, so i did but my check engine light came on. i asked the tech if i can use his obd reader to figure out y the check engine light is on, so come to find out its PO420 & PO430. Since i go to UTI i brought my car to skool to see if i can get help. overall.instructor said its possible vacuum leak but hes gon clear the.code.w da. obd reader,drive for a couple days to see if check enfine light comes on again.weel on da way home from skool light came back on...also went to schoos.napa auto part store to see how much a o2 sensor costs, at napa.its $800 for the replacement which is waaayyyy too.much, but yea can anyone help figure what to do?

 

that sucks and its hard to find. I had a 93 and removed all I could because troubleshooting it sucked