I have a customer with the above car having had a replacement alternator or two (Bosch) which I have checked with the local factors and is correct to car, it charges upon start up but after a short while the battery light illuminates and the message ' Power system service urgent'.

I found the following stored fault codes in the body control module which have cleared and stayed away:

DD21 LIN Bus 2 Incorrect signal
DD30 Control unit alternator incorrect comm's

I have scoped the LIN single wire communication connection off the alternator and on, both running and Key on/ Engine Off which is all the same and shows a good signal but at a max voltage of 3.5v which i think may be incorrect, I cannot seem to get the signal to change but otherwise ok.

I have checked a petrol XC90 and that signal was peaking at 12v LIN

Any known issues with these, I have requested more info than just a wiring diagram to fully understand the system control ?