BTW, if autozone won't do it for free, or its a pain to drive to one and have them do it, any walmart or autoparts store will have very inexpensive code readers (make sure its one that will give you the actual DTS code numbers -- not just clear CELs absent of the info!).
Something like this
http://www.newegg.com/Product/Produc...0KZ-0001-00001
I usually see them in either orange or blue -- just make sure it gives the actual codes.
It should be around $25 and an invaluable tool for troubleshooting problems! They generally come with a listing to look up the codes, otherwise you can just go here
OBD-II Check Engine Light Trouble Codes
There's links for generic codes as well as Nissan specific ones.
You may still have to follow up trouble shooting the old fashioned way (i.e., under the car with a flashlight and tools), but to get pointed in the right direction, using the OBDII info is greatly helpful!
Good luck!