Toyota Repair: check engine light came on, toyota corolla, negative battery

Question
I have a 2004 toyota corolla, recently the check engine light came on while i was driving. What do you think it could have cause the check engine light to come on? The car is still driving fine and there seems to be no loss in power. I really dont know if it was a loose gas, in any case if it was the gas cap how long will the check engine light remain on for?

Answer
The check engine light will stay on until it's reset by either removing the EFI fuse under the hood or by disconnecting nthe negative battery terminal, without knowing what the trouble codes are I can't be of more help except to make sure the gas cap is on and tight, if the light turns on again it should be diagnosed to find out what the codes are.