MY Dodge caravan's sliding closes and locks. When

I had the same problem. The issue is with the switch/sensor that is depressed when the door is closed. On mine, there was a white plastic "boot" on the end of the switch that had worn down/cracked. I went to the hardware store and bought a package of rubber tips (the kind that slip onto a chair leg, or end of a pipe, etc.) I pried off the cracked plastic piece and replaced it with the rubber boot. Viola, problem solved.

If your plastic boot is fine, or you don't want a do-it-yourself fix, the switch is easy to replace, and only costs about $5 at the auto parts store.