Nissan Repair: ENGINE LIGHT COMES ON, nissan maxima, pep boys

Question
I bought a 1998 Nissan Maxima some weeks ago.  The engine light came on,I took it to a mechanic that checked it on his computer.  I received a code P325 which was the knock sensor so far i have changed that.  After getting it back from the mechanic two diffent codes came up PO600 Serial cummunication line fault and P1446 Undocumented code.

I took it to another mechanic.  He said,  I could have put gas in the car while the engine was running.  I corrected that by, putting gas in with the engine off.  The light still came back on.  Thanks for your response.

Answer
Byrd,

Disconnect the battery for five minutes and reconnect it and the codes will be gone.  Now, remember that you cannot have the engine running with the gas cap open or it will throw a code.  On the serial connection error there seems to be a problem with the guys connector and not yours.  After you do the battery disconnect thing wait until you have driven the car a couple of days and you should have no more problems.  But, if you do take the car to Autozone or Pep Boys and get the codes read for free.