1994 Grand AM is unique where as it is between OBDI and OBDII, some people actually refer to the 1994-1995 years as OBD1.5 but this term was never actually used by GM or dealerships. This is how you can read the codes --> Check the connector where you would attach the scanner on your car. If it has the top two right most pins which are GROUND and pin "B" you simply need to short them and the codes will be displayed via the check engine light flashing. The car will display code 12 by doing a single flash-short pause-double flash-long pause. The # of flashes is each digit of the code. Code 12 is the default code to tell you the diagnostic system is working. Code 12 will be displayed 3 times then all other codes stored in memory. If your car is like most 1994-1995 Grand Am's it will be missing pin "B". Thus you will need to purchase an automotive scanner capable of scanning this unique year. Actron CP9150 will perform this task. The scanner kit comes with the scanner, software, and harness capable of pulling the codes, and IT WORKS. I've tried it. The Actron CP9150 is no longer manufactured but can be purchased new via eBay for ~$160. Actron replaced this model with a newer one which is ~$400 but isn't necessary to pull the codes. GM suggests using a Tech-1 scanner which was used by the dealership, so they can also pull the codes for you too.
NOTE: Autozone can only read codes via the shorting the pins method or OBDII compliant cars (1996 or newer). The OBDII system went into effect in 1996 and all cars 1996 and newer are compliant, prior to this year every manufacturer used their own system, connector, etc.