Pug 3008 - errors P023B and P0598 - am I on right path to fix it?

[longgo]

As some time passed I have manage to make some additional tests and seems unfortunately still not quite close to solving that main issue subject to the topic.

* ECU - replacement
So far what I get as info from internet, that particular ECU tend to have issues. Either in PSA or VAG.
That`a why I decide to get one second hand and clone the original. The "logic" behind that decision was based on known problems with voltage regulator or some burned or broken PCB tracks
It was done successfully :

After that been done the car start fine and about minute later once again the temperature gauge flew to 120° , the attention triangle lamp lid on, and sure pop up the message : engine overheated
During that process diagnostic program was connected and that is what was registered:

As extra "bonus" : once again the initial ECU errors - P023B and P0598 show short to ground .. Uh..
Disconnecting the temp. sensor (which by the way was replaced by the owner insistence) and the thermostat preheating plug did not make it better.
That lead to follow:

* once again cable loom..

Here is once again partial diagram, how 12V are supply to water pump control, oil fume preheat and etc (mark in blue):

and as you can see it should have only 3 branches on diagram. That good, but in reality I had.. 4!?

from 1 to 4 are the branches seen on the upper blue line, and hence number 5 is the wire that goes back to ECU..
Now was good time to test it different, and maybe not so scientific way : to cut each line and see if there is any difference:

I have to cut the wire close to that junction and check if the errors where present or not..
One of that two wires from the common point, and what goes toward the intake collector, brought small success. Finally managed to see the ECU to be error free after engine been started.
Even unpluged manually the oil breather heater, can be also issue with the plug itself.. who knows but anyway at least for now the errors where cleared.
Yet, still the overheat problem was there.

* fan control
That was next in the list. And to reach that module the bumper also have to be taken down:

The diagram I use:

If I manage to read it correctly, the only one unit who actually control that fans is the engine ECU.
Checking over the diagram, marked in red it looks like thermistor.
And over the real unit looked as that:

With that module disconnected, right away the ECU throw error code, that the cooling fan control connection is missing.. New module was taken because of that suspected potential problem with thermistor relays.
After new module was fit and engine started once again the exactly same overheat issue pop up!!

And despite that crap, after few start ups the car refused to crank because the starter refused to engage at all..
Once rotated to ACC position I got message for a problem with the electric park break module. Oh boy! What the heck was wrong with a simple manually operated hand-break!!??
Not only that but there were also errors about no communication with ABS module and steering pump control module.. Daaaamnnn...
Also the dash board lost connection with the engine ECU and it went as that shot:

* battery control module

that one:

The problem now is that when the key is out of the ignition barrel and doors closed, on both bolts marked with red arrows I have 12.5v.
Once put the key to ACC position, right away the voltage drop as it is shown on the picture above..
Just for the test, I made a small jumper cable and bridge both bolts as it is shown on the right side of the image (red mark).
With that bridge on place and key switched on ACC still there was some light related to the parking break, but overall all errors in the modules where possible to be removed.
All errors cleared, then tried new engine start. This time no errors or lights pop up. Also in about 2-3min engine run did not pop up the heat problem or errors.
So now that battery control module will be replaced too and we`ll see how it will be after that..
To be continue..

[MattBLancs]

Quite a saga, good on you for persisting fighting it! Hope battery module is the key to it!

[longgo]

Hopefully will be the last pin in the coffin, because if that is replaced and all start popping up again, then really i`m out of any options and most definitely ideas..

[longgo]

Here is the current state, in case someone still follow.

The battery module was replaced with new one from AliEx for about 65e and change. Overall work fine.
Car started and worked quite normal, but again there was a catch: After it reached about 68°C as usual temp gauge needle went over 120°C and fan kick in on max! And sure enough there was another two extra errors related to the fan itself : cooling fan open circuit!

Fast test by activating the fan via computer showed that the LOW speed do not engage at all, and test over the HIGH speed activate the fan but end up in both cases with "open circuit".
At that point I return the original fan control module and what you know: the fan come to it senses and no "OPEN CIRCUIT" errors where stored. Huh!?!
Wire loom was tested for conductivity and resistance - all seemed fine.

Despite that small victory, still had the same persisting issue: 3.5V over the supply cable what feed the water pump control actuator, electric thermostat and etc. (see the blue line over the ECU diagram few posts above)
I also consider the following: once the engine goes up above some temperature, ECU put it into some pre-build emergency state because the pump can not be controlled by only 3.5V and it throw the that overheating message and kick the fan on max speed so the "user" will cut off the engine. Well also with bunch of error codes related to short or open circuit with all that mentioned parts.

This time had enough from that nonsense and I took different approach: with needle pin penetrated into the multiplug (that one)

voltage was fed straight from the battery. With that connection made, engine was started again and run fine until it reach up to 93°C.
This time it put the fan on low speed, no errors, no alarm, and.. so far nothing..visually burning
Now was the time to check up a little again:

pin 29 looked fine. At least what I can see, so I had to make one extra "bypass" :

That supplied enough power and is off when the ignition key is out. One new engine spin up to 90°C , again it was fine and no issues..or error messages.
Not sure if there is "improvement" but for now the car looks again a bit useful.

Despite pin29 seems fine(ish), will not come to a surprise if one of the power supply lines between BSM and the ECU is not exactly as it must be.
What I mean by that? At some point in the past I had big issue with my Xantia`s cabin fan. It start to messing around from time to time, and one day in the rain it just stop. The problem was that connecting pin(the female side in the plug) located under the fusebox in the cabin. Due the high current that copper "spring" part of it got loosen and barely contact. Enough to make conductivity test with flying colors, but of course not working when have high demand.
Here I suspect that similar small square contacts due the current and heat get a bit loosen. That one what actually supply power to the ECU in the line needed for that water pump control unit, preheated thermostat unit and etc..
Come to that conclusion because no fuses burn, no smoke from the loom (thanks God!!) and no change in the state of the problem despite what I change like ECU and BSM!

At least for now seems to work. Will get some extra tests and small drive in the hood and see is there still any issue or finally get that Pug running..