1]Iam driving 1999 buick century and its saying,"engine service soon'' which indicating inside.So what I have to do.?pls guide me. 2]And also my heater though it blows but it will not give hot air even after 10mins and Iam dying on roads while I go my work in morning 5:00 AM.Please guide me.

If there is a service engine soon light on, then there are codes that need to be read off of the computer. One can get an obd-ii scanner for under $100 at Sears or walmart or get Advance Auto Parts or Autozone to scan for free.

On the second question, check that the heater core is getting hot on both tubes at the firewall (heater hoses 1").
If not, then the system needs flushed or the heater core will have to be replaced.
If they are getting hot, then there is a blend door problem.