On or before 1995 models:

How to test it when you find it:

Another look below:

When you find the adapter, jump A and B with a paper clip.
Next turn your key on but don't start.
Watch your check engine flash the code/s.

EXAMPLE: CODE 12: one long flash and two short flashes
CODE 13: one long flash and 3 short flashes

Note: code 12 is usually the first code you get and just ignore it.
Watch the code after code 12, that's what you need.

Let me know when you got the code so I can guide you to the fix.

Unsure if you have the right code?

Go to Auto Zone parts store and they will scan the code FREE for you.
They do it to encourage you to buy parts from them. The trick is to VERIFY
the code first by testing the codes before buying any parts and ATS can
show it to you when you become an ATS member.

For 1996 models and UP:

Go to Auto Zone as in the above procedure. Also when you get there,
ask the person who will scan it for you to show you the location of the
suspected parts so you get familiar with it. Don't buy anything till you
have tested it or you will be wasting your money.

To get a complete listing of GM OBD1 CODES, JOIN ATS

The list can be used on most GM vehicles such as Buick, Pontiac,
Oldsmobile, Chevrolet and some models of Cadillac.

When you join ATS, you will be directed how to verify the code so you can
SAVE by not buying unwanted parts.