4WD light On R51 2012

[TAHBRE]

Hello,

For 1 week, i've a continuous 4wd light on the Dashboard. The car was immobilized during 1 month with the battery deconnected. Before this period, i had not got this problem.
I have tried to verify all electric connections, tried to move between 2WD, all mode, 4LO etc ...
Just a thing, 4WD button fixed on 2WD mode, when i put the ignition "on", i see a furtive light with the mode 4LO (blink one time), then 2WD mode appears ...
Do anybody had the same problem? How can i fix this problem?

Thank you