C4 Picasso P0573 Brake signal fault open circuit

[Vikis]

Hello. I have a 2014 Citroen C4 Picasso 1.6 115 diesel semi-automatic piloted with 6 gears (robotized manual). I encountered faults indicating that the gearbox and clutch learning procedures were incomplete, along with a P0573 code. During the learning process, I couldn't engage automatic mode; only manual was functional. After disconnecting and reconnecting two connectors on the gearbox ECU, it began to work. I performed the full learning procedure, but the car still won't drive properly. After 1-2 km, it shifts into neutral, requiring an engine restart to drive another few kilometers.

The fault code is P0573, "Brake signal fault (switch/CAN) - Open circuit." I tried several brake switches, but the issue persists: the service light illuminates, and there's a beeping sound with the ignition on. The brake lights are functional. However, the switches I used were not identical to the original, differing slightly. Some were from older C4 Picasso models.

When checking live data, I found two brake signals in the gearbox ECU. When the brake pedal is pressed, "Redundant Brake (CAN)" shows "Activated," but "Main brake (wire)" consistently shows "Released." I tested the same switch on an older 2009 C4 Picasso semi-automatic, and it starts and drives without issues or faults. On that vehicle, the "Redundant brake" always remains "Activated," and "Main brake" shows "Pressed" when the pedal is depressed. What could be the problem? What should I check, and where?
Thanks for any help. I checked all the fuses, seems all good.

[BarneyRubble]

2014 switch works on 2009 version car - OK
2009 switch works on 2014 version car - Unknown / No.

Is this a case where the cars are ever so slightly different, but have same fitment for switches. Backwards-but-not-forwards compatibility? I wonder would fitting a Citroen OEM brake switch matched for your 2014 vehicle VIN be the next move? Suddenly both brake circuits operate as expected and the re-learning completes properly because "Main brake" shows "Released" or "Pressed" accordingly while "Redundant Brake (CAN)" shows "Activated".

Obviously, for a vehicle age 12 or so, do make sure all contacts are corrosion and dirt free and use electrical contact cleaner spray on all connections to ensure maximum chance of connectivity.

[Vikis]

Bought another one, a newer version. Nothing changed, still the same issue

[Vikis]

Anyone can help? I've tried a lot of brake switches, but nothing has changed. It's impossible to delete the fault