System check fail

Use a paper clip to connect terminals "A" and "B" together. Turn on the ignition switch, then count the flashes of the Check Engine light. Those two terminals will be the only two right next to each other in one corner of the diagnostic connector.

Here is a link to the page that tells how to read the codes, and what they mean:

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method