There is some confusion about the '88-'89 Reatta's two diagnostic systems.  Maybe this will explain the differences.

One system is intended to be a reference for the car owner to help him understand what the error messages mean that are sometimes displayed on the Reatta's CRT screen by the computer controlled systems. This system can be accessed by pressing the Status button on the bottom left of the CRT screen, and then selecting Diagnostics. Once on the diagnostics screen you can select from a number of items on the screen. When you select any of those items you will see an OK button beside them. If you start pressing the OK buttons you will be shown a display of what error messages would look like in the event something actually went wrong with your Reatta.

Those messages are for information only and are not an indication of a current problem with your car.

If you see error messages while accessing this diagnostics screen they should be ignored. If you are seeing error messages on the CRT while driving your car you can use the diagnostics system discussed in the next paragraph to aid in troubleshooting the problem.

The other diagnostic system, (Vehicle Diagnostics System), is intended for use by a technician to troubleshoot the various computer systems on your Reatta. That system can be accessed by anyone but it was not intended to be used by the average Reatta owner.

If you are not familiar with OBD-I engine control electronics you should educate yourself on how the electronics function before accessing the Vehicle Diagnostics System.

Instructions can be found here for accessing and understanding the Vehicle Diagnostics System.