Given PO579 be thinking at looking at the connectors and as you've done some cleaning) to do with the speed control unit first. Remembering codes are only indicators and can be phantom codes.
I have seen this with the grey connector not pushed home....not suggesting that is it but worth looking at. Usually its that simple.
As you've been cleaning or looking at the cruise control unit - termed "speed control unit" in the CRD FSmanuals (just in front of the brake booster) it is possible that the grey connector near the fender has become disconnected or is not fully home resulting in intermittent ops. This will absolutely cause your issue but not exclusively. It's a simple matter of clipping it home securely but they can easily get bumped.
Another seemingly unlikely item to check is (and I now it seems unrelated) the state of the tiny paper filter tucked in the front of the cruise control unit between the fender (mudguard) and the air filter body. Also suggest you check the turbo hose integrity from the sir box to the turbo intake. They are known to split over time at the turbo intake These can be had cheaply from idparts.
Have you cleaned the puck (on top of the driver's side rocker cover)? - also feeds captured ioil back into the base of the turbo intake hose 19mm id.
Also do a run over it to feel that all sensor connectors are clicked home.
Bruce, there is no bleed screw on the Mopar filter (OEM) head other than the one on the engine side. The procedure that works best is to pump until pressurised (resistance is felt at the large black mushroomed button) and then release the air through the bleed screw. Only pumping whilst nipped up. Release the pressure. Nip up and repeat. If in good or even fair order it is one of the easiest diesel systems ever to bleed.
I liked to release it into a clear hose connected to a clear plastic container that was all connected up with leuer fittings so no spill. but a hose into a jar will do just fine if you can steady it against a spill- some use a paper towel or cloth to catch the spray from the nipple. The idea is to repeat until it is rock solid and no air escapes when the bleed screw is released.
P1684 notes the battery was disconnected - which you said you did....so given the way these numbers are structured - could be related, hence, prolly nought to worry about. I couldn't find that number specifically in the books I have.
Once the fuel filter and head is cleared of air the engine side is self-clearing/priming. Its a nice system really (short pathway and loosely primed by priming the system's head).
Hope that helps you but only postulating (obviously).
