Check engine light came on 05 altima - 2005 Nissan Altima

If you are a DIY'er you can get a OBDII scan tool that connects to your laptop that can tell you the error code and allow you to reset your check engine light. This will save you $80 each time over going to a mechanic for a diagnostic. They are easy to use and will help you know what the issues are if you do have to go to a mechanic.
Check out http://www.fitityourself.netau.net/OBDII.html
Sometime the check engine light comes on if you did not fit your gas cap tight enough. You need a code reader to find out the error code to help solve your problem.
If it is something simple (like a gas cap) and you do not want to get a code reader to find out what codes (problems) your vehicle computer is saying there is. You can try disconnecting the negative battery lead for 5 minutes. This should reset your check engine light. If the light comes back on, you have a problem and can take it to a mechanic or buy yourself a code reader.