We do not have the Caravelle here in the U.S, but the EuroVan is the same vehicle and I will use that as my reference to guide you.
The first question is, is there a "Check Engine, " or "Check Transmission" light on? If so, have it scanned and post the code(s). That will aid greatly in giving you an idea of the problem. Until it is fixed, please do not drive it, as the repair may be easy now, but after continued driving, it could become very expensive.