1999 Dodge Caravan check engine light does not stay on

System not ready
indicate that the battery was disconnected and or the computer memory was reset
the way to solve this, is by driving the van for few day and about 100 mile or so

or you can do this :
cold engine 1st start,
start the engine and let it idle for about few min
try not to use the AC if possible
then take it on a long drive 50 or so miles combine stop and go plus free way driving
making sure you don't shut the ignition or all will reset
return back to the inspection bay and ask for retest
DONT shut the ignition leave it running
good luck