Chrysler Repair: P1684 and transmission limp mode, ground circuits, autozone

Question
Hi Roland ...

Your first reply was much appreciated.  On Friday, I picked up the van, they had it for 4 days with no fix.  The dealer invoice I received gave me the following information back

PCM reported P0500 and TCM reported P1684.  
Tested battery + and ground circuits to TCM while wiggle harness - OK.  0.15V drop through battery + circuits from TCM to chassis ground - OK.  From fuse to TCM 0.07V drop through ground circuits from TCM to chassis ground - OK. Inspected connections at TCM and IMP - OK.  Vehicle module scan and erased DTCs.  Installed check bulb on TCM Battery + supply and road test - OK.

This was the report I got back when they gave me the van back.  They charged me labour rate for 6 hours of diagnosis but problem was still there today.  On the first of the day, stuck in 2nd.  I shut off the van off and re-started immediately, and the transmission is fine.  

I did check for codes today immediately after the the problem surfaced and I only get P1684, nothing else.  

Do you see any inconsistency between what you suggested and what the dealer did.  As a non-expert, they seemed to do what you were suggesting.

Answer
Hi Bryan,
It looks like they verified the 12V supply and ground return from the tcm. My suggestion would be to see if you can get the codes yourself via the ignition key, or for free via a readout at an Autozone parts store, and thus keep checking to see if any other codes appear, as I suggested.
Because the power supply is under the hood there is no simple way to monitor the supply wire to the tcm unless you want to run some wires from a voltmeter or glow light to the fuse with a readout in the cabin so you can watch to see if you can 'catch' a 1684 'in the act'. Something will eventually appear, so when it does let me know.
Roland
PS: Please rate my answer(s) if you believe they are helpful to you. Thank you.

I attach our first exchange for reference.
P1684 and Transmission limp mode
Question: Hi Kevin, I am at wits end with my Dodge dealer. A recent transmission flush seemed to create a problem with my 2003 Grand Caravan 3.3L.  The transmission sticks in second gear when I start the van, but if I put it in park, turn off the ignition and re-start the van, the transmission behaves normally.  On occasion at highway speed 50 mph in 4th gear, it will rev out of gear, and drop hard into 2nd gear and stick again.  My dealer has had the van for 6 days on 3 occasions and cannot solve the problem.  They need help and I am now searching the internet looking for advice.  I saw a recent similar post on this website that looked promising.  The only fault code on the transmission is a P1684.
Answer: Hi Bryan,
The 1684 can occur by simply disconnectint the battery and that is detected by the PCM, but
if that code is attributed to be from the TCM, then it could be a problem with the battery positive supply to the TCM or the grounding of the module. The 12V+ supply to the TCM is from fuse 15 in the power box in the engine compartement. It would be good to check that fuse to be sure it doesn't have a subtle crack in it wire that is causing an intermittent flow of current to the TCM. It is 20 amp size, and located just to the rear/left of the transmission control relay. The current flows to pin 56 of the TCM plug on a yellow/red wire. That pin of the plug should show 12v at all times. Try shaking the wire harness to see if it provokes a loss of voltage momentaritly.
The ground circuit is duplicated from both pins 53 and 57 to a nearby splice and from there on a wire directly back to the - post of the battery. That is not a likely cause of current loss but you could verify the continuity from those pins of the TCM plug to the - post clamp, with both the plug and the clamp removed, and similarly shake the harness.
Of course simply disconnecting the battery will also cause the code which will only self-erase after 50-100 key on-off cycles. Other than that keep looking for codes. You might be able to get codes by using the ignition key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window of the cluster to see if the mileage reading changes to show 4 digit numbers which would be fault codes. If that in not productive you can often get a free readout using a plug-in code reader at an Autozone parts store. Let me know any new transmission codes (in the 0700's or 1700's) and we'll go from there.
Roland

PS: Sorry for the delay in answering but I just found your qustion in the 'pool' to which it had been referred by Kevin. Please 'rate' my answer, and where you see the question about 'volunteer of the month' please consider giving me a 'yes' vote. Thank you.