I felt this would be a good read for all Mazda owners.

http://www.parttrackers.com/library/1/93/98/

I recently acquired a geniune Mazda code reader off EBay, to use with my 88 929. I'm informed that code readers are of 2 types, to work with the standardized OBDII format, and earlier (prior to 1996) OBDI. The discussion regarding how to self check is very interesting, and describes how to use the unit I have, although the shop manual is more detailed and highly recommended! Haynes didn't produce a book for the 929, and Clymer's sucks, so if you can get a geniune shop manual and code reader, you are miles ahead in my book.