About 2 months ago I bought an '04 Xterra 4x4, 3.3 V6, Auto trans with just over 87,000 miles. I am new to owning a Nissan and searched the forum but still have a question. It has been running fine ever since I bought it(and still is) but about a week ago the Service Engine Soon light came on. I had it checked and engine codes P0430(catalyst system fault-left bank) and P0328(knock sensor)showed. After searching this forum and reading about same codes it sounds like it could be a variety of fairly expensive issues to fix. My biggest question, since I live in Iowa and we don't have to pass emission tests for registering, is, will it hurt the engine to keep driving for awhile or does the problem need to be pinpointed and fixed immediately. Thanks for any feed-back because it sounds like their is quite a bit of experience on this forum.