As Bass mentioned, you have OBD I and all you need is a simple paper clip to read the codes. Locate the ALDL (Assembly Line Diagnostic Lead). It is located under the driver's side dash. Insert paper clip between terminals A & B as shown below.
Turn key on, but do not start engine. The check engine light will begin to flash. The ECM (computer) will display a "code 12" by flashing the "service engine soon" light, indicating that the system is operating. A code 12 is simply one flash, followed by a brief pause, then two flashes in quick succession. This code will be flashed 3-times. If no other codes are stored, code 12 will flash until the diagnostic terminal ground is removed. After code 12 has flashed 3-times, the ECM will display any stored trouble codes. Each code will be flashed 3-times, then code 12 will be flashed again, indicating that the display of any stored trouble codes has been completed.
Thats all there is to it!
opcorn: