I tried to return to 8841 but can not because the bootloader is lower.

Not worked for me also. Now i will try with original sd card and original navcore, im gonna edit VIN number, change couple of settings, update car icon or something, maybe this will work.

How did you try to install the Navcore`?
If you want to install the 8.842 from scratch try this way:
Extract the original CAB or the patched version I uploaded,
Inside you will find
- IA0000700006swlimage0.zip
- IA0000700006swlimage1.zip
extract both to the root of your SD,
rename the ~tsystem to ttsystem,
Now the Carminat should re-install the Navcore.
A downgrade could be possible the same but I think the bootloader will not allow it.

Yes, thats the way for navcore. Its kind a stupid thing from TomTom Carminat to change something and your BT remote dont work. In my dealership they dont know anything about it.

I still do not have the solution but maybe a track. The " newsettings.dat " file. I retrieve the file " settings.dat " another gps and I renamed " newsettings.dat ." At start the Carminat this file is then deleted and the ttgo.bif file changes. Placed at the root of the memory card , the file can change the file content " ttgo.bif ." So I was able to change the time, language, icon of the car and color palettes without the remote control operation. Now I have to find how to change the VIN and put the bluetooth.

I know programs that can change the car icon inside the settings.dat file and GPSForensics even has a program to read this file out but AFAIK there is no program that modify the settings.dat.
The car icon is stored in plain text though.

Using the " handle my device " function with tomtom home , I can change the language , time, so I think I can change anything else. You can also change it with another tomtom and after putting it on the memory card Carminat . I tried and it works . Only the car icon is written in clear and I managed to change the language and time to get it working in the Carminat .

Still I don't think the Vin number will be stored in the settings.dat.
And even if so it would surprise me if the remote is linked to the Vin number in any way.
No matter which way you look at it, the Vin number should not have changed by using a different SD.
A user in the German section did some testing ages ago and swapped SD cards between two cars quite often but never encountered a problem with the remote.

The hardware architecture of the Renault cars has, as far as I know, a central multimedia unit, and attached units for other functions (radio, Bluetooth, Nav). When the units are set up in the factory, they enter the VIN number for each one of them (including the NAV unit, that is our Carminat). A wrong VIN may cause dysfunctional communications, explaining the lack of information for our bricked Carminat (no radio, no temperature) and the remote not working (the Bluetooth module, which is not included in the NAV unit).

The only weird thing is that the remote IS working when you have a navcore update card : when you put an update card in the Carminat, it is checking internal and SDcard versions, the Navcore is not loaded (it should be a kind of minimalist linux boot) and you have 60 seconds to choose if you want to update the internal memory. The remote is working during this period, and disconnects as soon as the system is loaded.

Is it possible (maybe) to change VIN (put back original one) on original SD card, then use TomTomHome2 software to change something in settings, then put back card to Carminat. Maybe this will work. What does ValueRatio= in ttgo.bif means? This is also changed in my case.

So after some investigations :
1/ I found a very handy tool to directly change the ext3 file on Windows : R-Link explorer (in French). You can not directly edit the files, but you can easily drag and drop from and to a virtual drive and save when quitting.
2/ newsettings.dat only changes... settings. Using an empty newsettings.dat resets the voice, maps, language, home... but definitely not VIN, device ID or deviceSN.
3/ in all cases, a new ext3_loopback or loopback.ex3 is created (dump of internal memory card) I don't know if it updates something with the existing loopack on the sdcard (according to people working with poi, it does load the mapsettings, but I can't check without remote). In all cases, ttgo.bif is overwritten (and there is no information about VIN except in ttgo.bif)
4/ when you insert an original SD Card, the ext3 partition contains fewer files (in particular no settings.dat). With the 10 step new SD Card, you get additional files / directories :
- contacts (empty)
- diagnostics (data : contains .bin log files from Renault CAN errors)
- logging (empty)
clmdata file
settings.dat file
5/ I have a navcore update SD card image, and the loopback within has this peculiarity that it does not contain ttgo.bif. I tried to add a ttgo.bif file within it, but the update does not work anymore with the modified ext3 partition.

I am currently short of ideas... next step would be to try to set again the Vin inside the hardware via the Renault factory procedure, I will keep you in touch.

A friend from Renault checked my Clio today with their in house diag tool. The MIU unit (multimedia) was connected to the NAV and RADIO units, each one of them having their own VIN. The NAV VIN was wrong, so he managed simply to correct it. Now the loopback file is returning me the correct VIN in the ttgo.bif file.

Unfortunately, this did not solve any of our problems. I managed to downgrade to 8.841 and up again to 8.842, but this did not reset the problem and I still do not have radio & temperature display, nor BT remote functionality. I am afraid something got really corrupted in the internal memory where the navcore is installed (where we have no access) so it might be very complicated to continue...

The main problem is that it is a in-car-system.
Sadly TT is like other GPS producers and only sell their stuff.
Once that is done the customer has the blame game.
Your dealer might be helpful up to a point but has no real clue about the navigation part.
TT will simply refer you to your dealer.
Both Renault and TT are aware of the Carminat problems but none of them is actively doing a thing to solve it.
With the VIN number now correct it means two things:
a) The units can be transfered from one car to another, so maybe it is possible to source a unit from a wrecked car.
b) Even with matching Vin numbers the TT is unable to access and address the hardware fully.
If I would not know better than I would say TT has to provide a "rescue" update, something like a proper hard reset, clear flash and format for the entire system.

Maybe your nice dealer would be willing to make an official request to TT to either provide a suitable update or at least tell them a working procedure to "mate" the GPS with the rest of the car again?

NojTorrent,you say you 've managed to downgrade in 8841 . How did you do? I want to try.

If you make a fresh install from the navcore_8841.453398.Carminat_TomTom.cab (you might also thy the navcore_8840.380186.Carminat_TomTom.cab, but in my case, I used 8.841), ie unzip, rename ttsystem, patch the navcore... and you update it using tomtom home, it will download a new navcore (you will have to delete ttgo.bif on the root of the SD or else the update will fail). This update card changed my system back to 8.841 (you can see it on the update screen and also after the update in the ttgo.bif of the loopback). Putting the card again in tomtom home and it will suggest another update again. This second update gives you an 8.842 navcore.