Hello, my 87 Cadillac has been sitting for the winter. i fire it up once a month. today i noticed after starting it the check engine light was steady on. What are possible causes for the check engine light to be on that i can look into. i only had it running for 3 min when i noticed the light on, so i turned the car off. it does have oil. and fluid in rad. i dont know much of anything about cars.