you ain't a kiddin'
A quick google search and it sounds like you jumper pins A and B and then count the number of check engine flashes.
http://www.troublecodes.net/gmobd.gif
Codes
How to get codes from a OBD I Use a paper clip to jumper Terminal A and B of the ALDL *Assembly Line Diagnostic Link* which is above your left knee.
Terminal A is an interal ground and is the top right terminal in the connector. Terminal B is directly adjacent and to the left of Terminal A.
Turn the ignition to ON.
All codes are 2 digits between 11 and 99. Codes are displayed on the SES light by flashing the light with short and long pauses to distinguish digits of one code from digits of another. The short pause is used between digits of the same code, long pauses are between codes. Also, each code is flashed three times before going to the next code.
For example, the sequence of code 12 will be: flash, pause, flash-flash, long pause, then repeat 2 times. If Code 12 is not displayed, the self-diagnostic pogram i snot functioning properly.
If only Code 12 is displayed, no system malfunctions have been stored.
Any existing system fault codes are displayed in order from low to high, except for Code 11.
On vehicles with an automatic transaxle and on which exist stored transaxle codes, Code 11 will be displayed last, then the SHIFT TO D2 light will begin flashing transaxle codes of flags.
*I have no idea what SHIFT TO D2 light is*
When all engine codes have been displayed, Code 12 will flash again.
Diagnostic Codes
11. Transaxle Codes present
12. Diagnostic System Check
13. Oxygen sensor, circuit open or not ready
14. CTS circuit, out of range high
15. CTS circuit, out of range low
17. PCM fault, pullup resistor
19. 6x signal fault, no 6x signal between reference pulses
21. TPS circuit, out of range high
22. TPS circuit, out of range low
23. ATS circuit, out range low
24. VSS circuit, no signal
25. ATS circuit, out or range high
26. Quad Driver output fault
32. EGR system fault
33. MAP sensor circuit, out of range high
34. MAP sensor circuit, out of range low
35. IAC valve, rpm out of range
41A EST circuit open
41B EST circuit shorted
42A Bypass circuit grounded
42B Bypass circuit open
42C Bypass circuit shorted
41. EST bypass, open or shorted
42. EST bypass, open or shorted
43. ECS (knock sensor) circuit open or shorted
44. Oxygen sensor indicates system lean
45. Oxygen sensor indicates system rich
46. Power steering pressure switch circuit, open
49. Idle rpm out of limit high (vacuum leak)
51. PCM memory error
55. A/D converter error in PCM
81. ABS message fault (1993 vehicles with TCS)
82 PCM internal communication fault
Diagnostic Flags
27. Quick quad driver output fault (1993 only)
48. Reference imput intermittent or noisy
52. Battery voltage out of range
53. ESC knock present
54. Five volt reference ground
58. Battery voltage unstable
61. 6x signal fault
63. Option check sum error
67. Handwheel sensor circuit fault
71. Cooling system temperature high
72. Coolinng system temeprature low
73. CTS sensor unstable
74. CTS/transaxle temperatuer sensor ratio error
76. ATS sensor unstable
83. Low coolant (1993 only)
