x164 GL450 Diff lock system overheated. Wait briefly

Firstly let me start by apologising if this issue has been discussed before on this model car. The admin can dome a favour and move this to the right post...thanks.
I have a 2009 GL450 Diesel, i have had this car for almost a year now, when i first bough within a week i had the rear speed sensor failed and i replaced it with (after market) and the magnet holding feel when turning stopped and all was well, but now every time i put the accelerator down to take off quick like at give way stop or traffic lights, i get a beep beep noise and on my dash i get a message (Diff lock system overheated. Wait briefly) and this will stay on for a mile or two and it will go off on its or sometimes it will go off when i have stopped switched the engine off and on again. (I don't if this issue used to be there before the sensor was replaced or not) This is annoying as i don't know wether by keep ignoring it and keep driving it am causing harm to the differential or something else? i have tried to plug it to a diagnostic machine and the only code that comes up is (right speed sensor carry out visual inspection) i have carried out visual inspection and everything seems fine no bent pins or damaged sensor or cable...now i don't know what it could be. Am being tempted to go and buy OE part from dealer and try to see if this goes but then what if it doesn't go and problem still persists. Pls if anyone experienced this before i will be more that happy to hear your stories or mainly your fixes.