C4GP Gearbox fault + Parking brake fault

[Elder]

Hi guys
I found the issue. It was the gearbox ground cable. It was broken next to the gearbox end.
Now I need to replace this cable. The part number is 9677717680.

The question is: After I replace the broken cable I need Diagbox for checking and deleting the possible errors? Until now I couldn't find anyone with Diagbox.
On the eBay, the Diagbox software is 40-100 pounds. Is working?

I found this because after I checked all the fuses (all OK), I start to check the wires.

Thank you so much for your help.

I can confirm that after a full day today changing the battery and replacing starter motor, I found that the earth cable was attached by only the plastic heat shrink sheaf and when I pulled it, it broke. I made a new connection and bam, the car started. Honestly everyone, check that earth cable, even if it looks like it’s attached. A little tug on it should not break this cable ever, if it does break, there is your issue.
Thank you Mike. Life saver. Good luck everyone.

[Elder]

People, check the earth cable on the gearbox end. You can see this by just looking through the gap between battery and engine. It’s attached to the back of the engine and can be accessible from the passenger side jacked up or by moving the module next to the battery out the way to gain more access. 13mm bolt.
Mine appear to be attached looking at it. However, a light tug on it discovered it was only connected by the heat shrink tube they put around the connections.

I replaced the battery and starter motor before I discovered this forum. Thanks to Mike above for discovering it.

[salmangus]

Hi all,

I have the same problem with my 2015 C4 Grand Picasso. It was in a workshop for body repair and was working absolutely fine until I received the call from the mechanic that car doesn't start anymore and showing loads of faults on the screen, they checked it with different diagnostic tools but none of them was able to communicate with Gearbox. Took it to Citroen specialist and he raised his hands too and couldn't find anything. Now car is parked at my home and came across this thread and as mike suggeted I took out the battery along with it's tray and found this 9677717680 cable still intact but exposed from the middle and I can see some wires are broken and croded. I did checked the continuty on this cable and it does have the continuty. The thing I am trying to ask here is that is it worth getting another cable and test it or the continuty means nothing and it still could be a bad cable.

Thanks.