what causes the check engine light to stay on?
The codes you get from the OBDII port will point you to your answer.
You can Google the code number(s) to find out what they mean or post the numbers here.
If you choose to post back with the numbers be sure to post back with all the information about your vehicle.
The light stays on because there’s a problem that hasn’t been corrected. Either follow @Purebred 's advice or just take the car to a shop and let them diagnose it and give you an estimate. You’ll also need to decide how much you’re willing to invest in fixing a 22 year old car in case it’s something expensive.