A 1988 is not an OBD2 Compatible car. OBD2 did not become the norm in the US until 1996.

Beyond that I cannot tell you how to use the diagnostic port on the car, but someone more knowledgeable will post and tell you how it is used.

If the car is OBD1 compatible, OBD1 is fairly limited in what it can tell you, its mostly emissions related codes. What issue are you having?

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