Don't you wish that yellow check engine light would just rest at peace, unlit? Tough to envision constant peace around the world, and also a car requiring no maintenance. I was ready to install a new oxygen sensor in my car, which is a 1998 Maxima, in response to the yellow light. Actually, I had already bought the part and rented the install tool when I found that Autozone would read the codes for free (parts bought at Autozone). Since the dealer or test station was going to charge more than the cost of an O2 sensor for a diagnosis, I figured why not just change at 70,000 miles and see if that fixed the problem. As it turns out, code said the problem was knock sensor. Perhaps due to running regular instead of premium gas for a few tanks. Research on the net revealed some info, but incomplete. For example, someone wanted to know if an inactive knock sensor retards engine timing. I believe the answer is yes, because after new knock sensor installed the car instantly ran much stronger, with less hesitation up steep hills, and also shifts better (mine is automatic). Don't hold off putting in a new knock sensor if you need one, it's worth the $150 part to have the car run so much better!! Can be purchased from Courtesy Nissan in Texas, find it on the internet. (Not necessary to buy wiring harness, just the new knock sensor part.) The other question regards installation. It's possible to do it yourself if you're somewhat skilled and have decent tools. Sensor is located on top of engine but under the intake manifold tubes. Can't be reached with normal size male hands unless take off electrical connection on right side of engine (when at front of car looking down). Unscrew small nut that is underneath the metal flange that holds the assembly. Be careful not to drop parts into deep recesses!! I had to explore to find the bolt I dropped when old knock sensor was being pulled out. Also, to reinstall bolt, it's helpful to place a piece of tape into socket so that bolt will not come out of socket when moving into position to install. Good luck and happy running!