lol just check the ECU. im sure its somewhere easy to access. In 240's they are under the passenger side kick panel, I think they may be next to your gas pedal in maxima's.

Either way, a 10mm socket will remove it, and when you have out out, turn the car on, but do not start it. Then take a flat head screwdriver and turn it fully clockwise, and wait a couple seconds, then turn it fully counter clockwise. The lights on the ECU, and y our check engine light should start flashing....

first its slow blinks, the number = the first digit (or 10 for 100's).
second set of blinks is fast, this is the second digit.

then there is a long pause, and it goes to the next code, or starts over again.

turn key off to end, or turn screw all the way back, wait again, and turn it back to original position to turn light off.

when you get your list of codes, i think most nissans are the same, here are some for the 240.

http://www.240sx.org/faq/articles/ecm_codes_doch.htm

let us know what it is.