Welcome to Allpar. It is very difficult to diagnose the PSD (power sliding door) without a scan tool like the DRB III. The PSD module can store useful fault codes that would help in cases of intermittent or obscure failures.
There are flash updates for the PSD modules and PLM (power liftgate module) for various fixes. I don't know if the problem you are having would be addressed simply by a module software reprogramming. If there are other vehicle module updates available, get them all done while the tool is hooked up. The latest and greatest software is usually the best. This is Chrysler TSB (technical service bulletin) # 23-004-03:
http://dodgeram.info/tsb/2003/23-004-03.htm
The Body Diagnostic Procedures book gives an overview of the system on p. 34 and a diagnostic procedure on p. 930. Wiring diagrams are on p. 1127.
http://oskin.ru/pub/chrysler-dodge/manuals/Service Manuals/2003_RG_Town&Country_Caravan_Voyager_Diesel_version/15871-rsbd_sgmldiag.pdf
A series of switches have to open or close in sequence in order for the door to operate. Any mechanical binding or interference (obstacle detection) will stop the sliding door operation for safety. The hinge pivots and slide rollers have to move freely.
Intermittent electrical can be very frustrating. This is where having the module that can store fault codes is a boon to aid in diagnosis.

 

Thank you for the quick and informative reply. My vehicle was purchased new in July 2003, so according to the bulletin, some software upgrades should have already been performed. If I disconnect the drive cable from the motor, the door moves very freely, actually sliding closed just from gravity. Manually testing the obstacle detection, it does operate very quickly and with very little force against the obstacle. The Dodge dealer charged me $260 when I asked them to upgrade the transmission software, which they did with the warning that there was no warranty that the upgrade would improve the operation (which it did) so I assume that their charge for the power door diagnostics and software upgrade would be similar.

 

I have an electric sliding door on my '02 Grand Caravan that would unlatch but not open sometimes, as well it would NOT close electrically, as in it would auto-reverse when it got to the point of trying to latch down.

I thoroughly cleaned and lube the tracks and mechanism. Perhaps the biggest factor was cleaning the seal and metal surfaces the seal seals against, they were sticky with goo (small kids, you know), just scrub them with a wet soapy rag. And the door would work perfectly till a long trip filled with snacks and spilled soda's, etc and the door seals got all gooey again.

 

A 'diagnostic fee' is usually about 1 hour labor which is usually also the 'minimum charge'. The terms should be stated in writing at the service desk. Around here, that can be in the $80-$100 range. When compared to 'independent shops', the charge isn't much different.
They will contact you if the labor for diagnostics rise above that charge. It is possible that no parts would be needed for the repair. On the other hand, an intermittent switch might be serviced as an expensive complete latch assembly. If that is the case, you could decline the repair and do it yourself (with a good used part?). You would then just pay for the diagnostic fee that required a DRB III to troubleshoot.
If you decided to have them perform the repair, the diagnostic fee would be applied toward the total bill as a labor charge.
If the door is able to unlatch, that is called 'pop off'. Another (pawl or ajar?) switch takes over and signals the PSD module to run the door slider motor and that may or may not be happening. It does behave like an intermittent switch issue. A stored fault code may point to which one.

 

It does sound like an intermittent switch type problem, but without taking the latch assembly out I could not tell if the switches could be replaced with standard parts or if it is a custom item. In my experience, the dealer always replaces the largest possible part assembly because its less labor for them and less likely to end up as a recall so they would probably want to replace the entire latch assembly. There is a used one on eBay for $60 including shipping, less than the diagnostic fee. If I pay with PayPal and it does not work properly I can return it for a full refund. By the way, the breakdown of the bill for the transmission software upgrade was $110 diagnostic fee, $110 software upgrade, $40 bench charge.