This is my first post in this forum and I am no car audio expert at all, so please do forgive for my language.

My problem is the following:

I own a Volvo V40 car. It has 2 front speakers, 2 rear speakers and a subwoofer that is coupled to the rear speakers. That is: the level of the subwoofer is controlled together with the level of the rears: rears louder means subwoofer loude, too.

Perfect for me! That was with my Alpine CDA 9853R.

Now I switched to an Alpine iDA X001.
I unplugged the "MultiPin" connector from the old 9853R and put plugged it into the new X001.
Everything works, except for the subwoofer!
How is this possible? How can I change this? I don't want to use a separate amp for the sub, I like the sub to be controlled with the rear speakers.

Can anyone help?