Forterra 140 HSX rear differential lock problem

Hi guys. I have Forterra 140 HSX when the rear differential lock is turn on after 5-10 sec it turn off itself. After 5-10 sec it trurn on itself. So it turn in turn off, turn in turn off. There is no strange voice. When I turn it manually i can hear pressured air voice it is normal. But when it turn off itself there is no pressured air voice. So I think no problem with air compressor, because the barometer measure is good!

Do you have any idea where is the problem?

I have a HSX 140 myself too. But have to admit I never used the diff lock on it. When you say not hearing strange voice??? do mean strange noise! It's like you getting an air leak that's cutting out.