Default [Q] Kindle Fire HD P48WVB4 won't fastboot

Hi,

I have a brand new Kindle Fire HD Modell number P48WVB4 with 11.3.2.1 installed and I want to root it.
But I have the problem that the device won't boot into fastboot.
I have built a fastboot cable where i jumpered pin 1 and 4.
When I plug in the cable it starts but not in fastboot modus.

Any ideas?

Thanks in advance,
Daniel