Strange problem, PCM no communication - 2014 Dodge Ram 1500

Second attempt for better resolution
 

 

This shows TCM input voltage (red) vs current at the LR Solenoid.

Interesting. I have questions. I will post, again, this evening.

My first question was going to be about the voltage. But, then, I realized that you are using an attenuator. 
Your screen shots are of an actively pulsed solenoid. That makes it a bit harder to read. A single, clean, On/Off event would be more telling. You should be able to capture a single On/Off event by turning the key on, without starting the engine. 

Here is a Copy and Past from Alldata:

Theory of OperationThe Transmission Control System uses five electronically controlled solenoids that allow hydraulic fluid to be applied to various friction elements (clutches), which enables the gear requested. The continuity of each solenoid circuit is periodically tested. Each inactive solenoid is turned on for a few milliseconds, then off. Each active solenoid is turned off for a few milliseconds, then on. This pulsing of voltage to the solenoid causes an inductive spike which is sensed by the Transmission Control System. If an inductive spike is not sensed by the Transmission Control System during the continuity check, it is tested again. If the test fails four consecutive times, the appropriate Diagnostic Trouble Code (DTC) is set.When Monitored and Set ConditionsWhen Monitored:

1. This diagnostic runs initially at power-up and every 10 seconds thereafter.

Set Conditions:

1. After four consecutive solenoid continuity test failures.

Here, is a link to a video that I made about a year ago that illustrates this.
drive.google.com/open?id=1Q5G8Q5-v-yrvEY...tGwog8G&usp=drive_fs

Also, I would turn your scope sample rate up to 1 MS/s.

 

Hi Chad, Following up about this solenoid issue.  Somehow I missed your post linking your video about the P0750.  Too bad as it would have saved me a bit of time, but I came to the same conclusion.  Your video was an excellent description of the problem.  Attached are my screen captures showing the current and voltage waveforms between a good and a bad solenoid.  Your explanation of current ramp will be very helpful in the future.  

 

I am continuing the peel back the layers of strange behavior from this truck.  I also found that the line pressure sensor was broken off.  I replaced the line pressure sensor with an aftermarket parts store one and now have P0934 Line Pressure Sensor Circuit Low code which sets within a few seconds of driving the truck after clearing the code.  I appear to have circuit integrity and the scan data looks reasonable.  Scoping the signal wire reveals a low sample rate pressure transducer with lots of spikes in the signal.  I plan to replace with a Mopar sensor to see if this clears the P0934.  Should have the sensor tomorrow and will report back.  

However, the really weird symptom is that the truck shifts normally through first and second gear, but 3rd gear is a neutral shift (engine free revs).  However, this does not appear to be a mechanical problem with the transmission.  If I use the manual gear selector buttons to select 3rd gear on the cluster, the transmission will shift through first and second and then shift to third normally and hold.  When shifting from second to third, the PCM should turn the 2C Solenoid off and turn the 4C Solenoid on.  I monitored the 4C Solenoid control wire with the scope while replicating the neutral shift symptom and found that the 4C Solenoid does not turn on as part of the 2nd to 3rd gear shift event.  I also found that the Multi Select Solenoid switches off for some time during the shift event and then begins to modulate again before switching off until the truck is allowed to slow down and shift into 1st again.  2C Solenoid does switch off as part of this shift.  

I can't think of any plausible reason why the PCM would command the shift properly in Manual mode while failing to apply the solenoids correctly in Auto mode. 

Attached are some attempts to capture the relevant sections of the behavior of the MS Solenoid and the 4C Solenoid during both a successful and an unsuccessful shift.  

Reposting trimmed images.

For reference, here is the solenoid application chart for the six speed RFE transmission.

 

I'm glad that read that you are making progress!

I can't think of any plausible reason why the PCM would command the shift properly in Manual mode while failing to apply the solenoids correctly in Auto mode.

...

I plan to replace with a Mopar sensor to see if this clears the P0934. Should have the sensor tomorrow and will report back.

Let's see what happens with the new Pressure Sensor. Let us know.

New pressure sensor installed. I figured out that the old sensor's signal voltage was about .1v at 0 psi whereas the Mopar sensor was at .5v at 0 psi. Looking back at service info, the code sets if the signal voltage goes below .35v for a certain amount of time. So, defective sensor, and no more line pressure code.

However, the shift symptoms are still the same.  I now have only the P0733 after the neutral shift.