Transmission fault while driving, Peterbilt 579

First thing to do would be to carefully check all the wiring coming from the transmission. Pull apart any connectors and look for corrosion. Even if no corrosion best to clean with a cleaner such as Deoxit and then use silicone dielectric grease before re-connecting. The Eaton website has complete diagnostic manuals that can be downloaded for free. The manual gives diagnostic procedures for each code. Almost 400 pages so too large to attach here. After checking the wiring and connections I would clear the codes and drive to see if any come back. May have just been a loose connection.
The ECA was not getting the voltage it needs.
The code in the 2nd pic, 520271 FMI 4. Your link tells what to check for that code and FMI 4.
The ECA operates on a non-switched battery power supply.
FMI 4 – Voltage Below Normal or Shorted Low:
FMI 4

• ECA Vehicle Harness
  • Damaged wiring between the vehicle batteries and 3-Way ECA Connector
  • Bent, spread, corroded or loose terminals
  • Wiring shorted to ground, shorted to power or open

 

I drive a Chevy Silverado, and I ran into a somewhat similar transmission issue last year. It started acting up on the highway, not wanting to shift properly, and then I got stuck with it not going into reverse or drive, just flashing symbols at me. After some trial and error, and almost thinking it was a major mechanical failure, I stumbled upon a solution that involved checking the connectors and wiring, much like you did.

What really helped me diagnose and understand the issue better was using cummins software. This software gave me a detailed analysis of what was going wrong and pointed me towards a problem with the connectors and a potential wiring issue. After securing the connections and checking for any wiring faults, my truck started to run smoothly again.

 

Ok. Same issue on a ‘22 579. I’m under the transmission and finding no ECA as described in the schematic. No, I’m not a wrench, but I can follow directions. I’m finding nothing in the location shown in the diagram linked above. These connectors are external, correct? Any assist would be appreciated. Trying to avoid being stuck in some POS while mine sits in some shop gathering dust. Thanks.

 

If you’re not aware, PACCAR are notorious for their shift stalks failing at inopportune times, like stop signs and stoplights. Mine even popped into neutral, on the interstate, with the cruise set. The randomness of their different faults will drive the unknowing crazy. I’ve had it in my T680 and my buddy’s 579 started doing it, shortly after.

 

Get the latest TCM update installed.

With backing, I use my right foot to apply just enough throttle to engage the clutch and my left to modulate the brake, keeping me from slamming the dock. My 1st pickup is uphill into their dock, so I had to relearn some things, after being in a Volvo. PACCAR are the worst.