Hi Anthony Thank for all the help in the past with my 1992 Diamante unfortunately I don't have it anymore. I bought a 1995 Nissan maxima{I know that it is not a Mitsubishi} My question is my check engine light is on and it reads that it is my knock sensor what is a knock sensor? and how important it is? and should I get it fix right away?  

A knock sensor counts the number of knocks or pings it "hears" when your engine is on. It sends this information to the car's computer (ECU). If the ECU determines that there are too many knocks heard during the engine cycle, it will delay (retard) the engine timing. When the timing gets delayed, your engine will not produce as much power. Your power will not be regained until that knock sensor detects a count within it's normal limits.

Engine knock usually occurs when your engine is not receiving the correct octane of gasoline. Check your owners manual. My father has a '97 Maxima, and the owners manual specifies to use premium (high-octane) gasoline. High-octane gas is used mostly in higher performance engines, and engines that require much higher temperatures to completely burn all the fuel that enters the engine. The big misconception about high-octane gas is that it makes your car go faster. Premium gas will not make you car go faster, but if it's recommened by the manufacturer, then you should use it.

My guess is that the previous owner(s) of your Maxima either didn't know to use premium gas or just didn't want to because of the higher cost. But the few cents more per gallon for premium gas will allow your engine to run at its full performance. And merely using regular gas will cause your knock sensor to continuously be counting, working overtime, and eventually will wear out.

You should get your knock sensor fixed. It won't ruin your engine right away, but can cause severe problems if continued to sit, and not being replaced. It's typically not too much of a hassle for a mechanic to replace, but that's just what I know from my Mitsubishi experience. I've never had to replace it on a Nissan.

Get it replaced as soon as it's convienent for you, and only use premium gasoline if your owners manual instructs it.
Good luck!