There are a bunch of things that could cause the check engine light to come on. Yes, being a '98, it has OBD II. Being a chevy dealer, they probable don't have the universal scan tools like independent have to read OBD II info. I work for a MB dealer and our software in the SDS will not communicate with, lets say, a 2000 chevy impala. They can take it to Autozone, or wherever, like you have done in the past and they could read the codes.