The ?check engine? light came on, what does this

You will never pass a smog test if a check engine light is on. The light being on says you failed before they did anything to your vehicle. Take the vehicle to your local autozone. Autozone will scan the vehicles computer and get the codes that are causing the issue, and they will do it for free. After you make the repairs, you will need to get the computer reset. Autozone will also reset it for you for free.