i just bought this 1999 nissan altima and yesterday i went and put gas in. 20-30 minutes later my service engine light was on. there are no noises coming from my car. its under warranty but i seriously just bought it 2 days ago. any suggestions
Take it back, have the code(s) read and get them to fix it. (I assume you put the gas cap on tightly.)
I don’t know where your confusion comes from. You’ve only had the car for two days, but it’s been around for somewhere around 4,300 days. Anyway, brand new cars sometimes have faults discovered on the first day of ownership.
well i was planning on taking it to auto zone to have them hook up to the computer in it.but putting a gas cap on too tightly can make that light come on?
Not tightly enough can - it is suspicious that it happened just after you put gas in. Make sure it “clicks” a couple times to make sure it is on tight.
The reason it goes on is the vapor recovery system keeps gas vapors from escaping, but the system needs to be closed to work, if the gas cap is loose, air from outside can get sucked in keeping the system “open” so it cannot capture the fumes like it should.
If that is it, tightening the cap will cause the light to go out after some number of starts (not sure the number, but a likely a few days worth)
i thought it was weird after the gas too. and i will check. i think i will still take it to auto zone. never hurts to be safe. thanks for your help though 
Service Engine Light or Check Engine Light?
If it is a Service Engine Light, then you are do for maintenance, like an oil change. Check the owner’s manual about it.
If it is a Check Engine light (CEL) then have the codes read and post back with the actual error code like [P1234] Note: CELL’s DO NOT tell you to replace this or that part. At most it is tilling you that it is getting an unexpected message from that part.