I picked up a 2006 Caravan,

Spooky. Some of these had no memory retention, so if it doesn't run and nothing works it will need to be "flashed" by the dealer. Runs around 160 bucks in my area. But if you put a battery in it and it starts and runs then it has memory retention, so no need for a "Flash". Now if it is a hard fault the light will turn on right away after engine start, if it's a soft code then it will turn on right after the system goes into closed loop, anywhere from 10 to 15 minutes depending on external temperature. HTH

If you don't have a check engine light after 2 or 3 days of driving, with the gas gauge between one quarter and three quarters, scan the computer and look at the readiness monitors. If any are not all set, continue driving it and see if the check engine light comes on in another few days. If not, scan the computer again. If all readiness monitors are now set and you have no check engine light on you're good to go. But remember, you must keep the gas gauge between one quarter and three quarters for the computer to run the diagnostics on all the systems. Jim