Volvo xc40 amplifier

[Lukas]

That is strange, both AUDs shows the same SW part and configuration numbers. 
What is you OEM settings for 028 ? 
If it's 01, put it to 02. 
If it's 02, (less likely) put it to 04. and reset the IHU and AUD. 
If still you cannot hear from pin 02 (-) and 09 (+), either your IHU does not have the software to enable the AUD or the AUD you both is faulty. 
Send an email to support, they might have the pre-amp software for your IHU to enable it.

OEM 028=1.  that was the original.  I wrote for support.  so if I can, I'll install the software.  I hope it helps.