I have a 97 STS that I just did the head bolt insert and top end gaket repair to. I have replaced both exhaust manifold O2 sensors and now when I clear the codes on the MIL it stays gone for about 15 miles but then the SES pops up with all O2 codes. I am hoping that someone can help. I have a great deal of time, money and effort into this and all I have to do is make the codes go away so that the SES will stay off so that I can smog and tab it. Thank you to anyone who can help!