ok my check engine light is on.....so i ran a scan said the o2 sensor was bad. replaced the bad sensor. now should the check engine light automatically go off or should i disconnect the battery n let it sit for awhile n re-adjust?

Yours is a 99 model. You will need to erase the code with a scanner or it will remain on for about 50 engine start cycles.

how hard is it to erase it with the scanner

Plug in and push "Erase". AutoZone will do it for you for free.

That about covers it.. ^

ok, if my heater isnt blowing any air, would that cause the check engine light to come on? n if so when i do erase it how long will it stay off

do a search about that... its been covered not too long ago.

ok, if my heater isnt blowing any air, would that cause the check engine light to come on? n if so when i do erase it how long will it stay off

No.