Strange problem, PCM no communication - 2014 Dodge Ram 1500

Hello, 

I am working on diagnosing a strange issue with a 2014 Dodge Ram 1500 5.7 6 speed automatic.  The truck is a no crank no start.  There is no check engine light on the dash with key on and I cannot communicate with the PCM.  I can communicate with all of the other modules and have scoped the CAN bus, which appears to be operating normally.  No codes are present in the other modules except for "lost communication with PCM."  I purchased a second used PCM for the vehicle which behaves the same way when installed.  

I have bench tested the two PCMs to see if they appear to be working properly.  When powers and grounds of the PCMs are connected to a power supply on the bench, a change of state is observable at pins 7 and 80 (pin 7 is energized by the PCM; pin 80 is grounded by the PCM).  These state changes energize the Powertrain Module Relay and the Auto Shutdown Relay, respectively, which feed power to other circuits of the PCM.  

When I install the PCMs in the truck, I measure key on power at pins 96, 47, 23 of C1 of the PCM--however, the state change on pin 7 does not occur, and therefore power is not supplied to the Powertrain Module Relay, and the PCM (presumably) does not power up.  

Because I was able to detect the state change on the bench, but not in the truck, I devised a system of bridging individual pins from the PCM to the PCM connector with breadboard leads.  When I bridge only the powers, grounds, and CAN C lines, the state change is detectable, the PCM powers up, and communication is restored.  However, when I again plug the PCM connectors directly into the PCM, connecting the rest of the pins, I get no communication.  

What could be causing the PCMs to not change the state of pin 7 and not power up when the rest of the circuits are connected?  

Please let me know if you have any questions about this situation, and thanks very much in advance for your thoughts. 

Check your 5v REF. If it gets shorted, it can cause a NO COM with the PCM.
 

Thanks for the reply. I checked for 5v ref on the bench at C2 pin 87 and the PCM is putting out 5v ref, but have not checked these circuits when the PCM is connected to the truck.

On the PCM, C1 pins 69 and 93 are labeled 5V REF. C2 pin 87 is labeled 5V SPLY. I’ll check those tomorrow. Let me know if there are any others to add to my list, and I can post screenshots of the PCM diagram if helpful.

5v ref checked. I was not able to find a short. I made sure all 5v ref circuits were disconnected from the PCM (PCM C2 disconnected; APP, AC Pressure Transducer, and Fuel Tank Pressure Sensor disconnected). The PCM still does not power up.

I should mention that I am able to make the PCM power up using the truck's power supplies with PCM C1 not plugged into the PCM by bridging individual pins between the PCM and C1 using breadboard leads. If all of the powers, grounds, and CAN lines into the PCM are connected, the MIL will illuminate with key on and the PCM will communicate with the scan tool.

My search for what circuit on PCM C1 could be bringing down the PCM comms continues.

I am able to make the PCM power up using the truck's power supplies with PCM C1 not plugged into the PCM by bridging individual pins between the PCM and C1 using breadboard leads.

This makes me suspicious of pin fitment. If the female terminals of the connector are too loose, it can cause connection issues. Are the male terminals of your breadboard leads larger/fatter than the PCM connector pin terminals? If the female terminals of the wiring harness are too loose, it will cause connection issues.
 

I had the same thought, and measured the pins of the breadboard leads to be thinner than the pins on the PCM. Pins on both sides thoroughly cleaned with DeOxit. I have also gone through with a tiny welding wire file and dragged it through each female pin--all seem to be exerting similar pressure. The problem also doesn't respond to wiggling the PCM connector with the connector partially seated. None of these definitively eliminate pin fitment. I suppose I could bridge all 96 pins between the PCM and C1 at once and see if the problem is present then or not. Are there any other methods to verify pin fitment is or is not the issue?

Are there any other methods to verify pin fitment is or is not the issue?

It is not always easy to do so, but if you can open the PCM, you can test voltage drop from the wiring harness to the back side of the PCM connector, internal to the PCM.

Looks like opening the PCM will be tricky but I will keep it in mind as a last resort. I do have a spare PCM for the truck I can sacrifice in this way if needed.

I am considering for a next step trying to disconnect every component fed through C1 as well as looking for shorts to ground on each wire in order to isolate the problem to the PCM power supplies and pin fitment.

The other major set of components on C1 is the transmission solenoid pack. Would it be possible for a short here to activate circuit protection and prevent the PCM from powering up?

The above tests may be a waste of time as the PCM may not be attempting to power up any of those circuits. Is there any other circuit besides a shorted 5v ref that could be preventing the PCM from powering up?

Thanks for all of your ideas so far.

Luke

I think I have finally isolated the problem to pin fitment at the PCM C1.  Bench testing the PCM,  I found that only pins C1 96,47,23 and grounds are necessary to power up the 5v ref circuit and CAN.  This paved the way for the next experiment, the aim of which was to prove that there was no other circuit on the truck "bringing down" the PCM.  I identified every circuit on the truck that connected to the PCM via C1.  After unplugging each sensor/component that was easily accessible, I was left with 11 pins that should still be connected from the truck to C1.  Using breadboard leads, I then bridged the PCM and C1 at pins 96,47,23, grounds, CAN high and low, and these 11 remaining pins.  In this state, the PCM powered up, the MIL illuminated, and the radio turned on (before it had displayed a theft mode message).  If my diagrams and work are correct, this proves that no circuit is "bringing down" the PCM and that the issue must be pin fitment at C1.  Fitment at the CAN lines is suspect, as are 96,47,23 (C1 Pin 7,as well as the 5v ref signal have powered up intermittently at times during the process).  

The next step is to depin the connector and install new female pins or crimp the existing pins to create more pin drag.  Hopefully a post is forthcoming confirming the fix.  And resources or tips on how to depin one of these Chrysler 96 pin PCM connectors would be appreciated--it's not immediately obvious how to do it.  

Thanks, 

Luke