1998 Volvo S70

First thing is first. Reading codes is not the same as diagnosing? I can tell you that you have an oxygen sensor code but that does not mean the oxygen sensor is bad? You can have fuel pressure problems maybe an intake leak problem or something else that works with that component? Codes only try and guide you to where you should look and see how that component works and interacts with other sensors? If you had it diagnose then I believe you would already now what the problem was? Are your codes engine management codes, transmission control codes, anti lock brake codes? What did they actually tell you that you needed after the diagnosis?