Check engine light

I get a check engine light on in my 94 Buick Century. It has a 3.1 engine. I've checked the fluid levels and everything is fine. Sometimes after driving it a certain distance it goes off but comes on again when the car is restarted. I've been looking for a code reader for this vehicle but it seems to fall between the cracks as the readers I see are for Centurys up to 93 and 95 and up. Does anyone have an idea on how I should proceed to resolve this problem.

Must be scanned on a scanner capable of reading codes for 94. AZ cannot do this.