My Dodge 2008 Grand Caravan automatic tailgate door will close and then release not locking it in place. Does the mechanism need replaced

SOURCE: 2005 Dodge Grand Caravan - Battery Replacement

no as long as its not over 15 mins

SOURCE: 2002 Dodge Grand Caravan Driver Door Lock/Unlock Switch

sorry not sure the 12v prob will help this swtich works on 5v off 3v unlock 1v lock single wire lock/unlock logic signals
I found wiring diagrams at
http://www.dodge.com/bodybuilder/2004/docs/wd/rswd/tc.pdf
it is 2004 but use the wiring diagrams to test the wires
(most likely to fail where they flex)
because it is using logic gates disconnect the plug at each end of the wire you are testing or the damn thing will find a few diffrent ways to trick you.

SOURCE: Spare tire location?

With the new 2008 models, the spare tire was moved from the rear of the van to a spot below the front seats. The lug for the tire winch is located under a round cover in the floor just in front of and between the two front seats. If you look under the van, you will see the black tire-shaped cover for the spare.

SOURCE: 2005 Dodge Grand Caravan: Power locks noise

the door lock actuator is going bad.

SOURCE: How do I replace door lock actuator on my 2002

Which door? I can advise on drivers side sliding door.