The check engine light was on, it came back with a P0134 code, so we replaced the 1st O2 sensor,not knowing that it is not necessarily the sensor that is bad. It didn't fix the problem. Then did some reading, checked fuses, replaced some, cleared the codes from the computer. So, now the P0134 is gone and is throwing a P0135 code, which I guess was already there but just not showing on the screen. So, after more reading I have a question. I know the next step is to test the voltage coming from the O2 sensor while it is hot. But, if the voltage is incorrect, how do we correct it? Also, if it is correct, what is the next step? Any help would be greatly appreciated.