Autozone stores will tell you the number of the code for free. About.com has lists of what they mean, you'll have to search for the model car you have. or you can Google search for the code and try to find a common theme in what you read on various message boards http://www.nissanforums.com/forumdisplay.php?f=24 I think that URL should help. It should take you to the b14 Sentra forum. The first topic on the list was the ECU error codes. There are also other service tips there too.
35mm - 40mm
Depends on the size of the engine and what part you are using, but in most cases yes.
.044 for a 1997 model
You don't, it has a chain.
NO SE TU....
It is located in or on the transmission.