Volvo assures me there is no code necessary for my radio. Car sat with dead battery for long time, radio screen comes on occasonally. If you switch car off and on 6 times, screen will switch off and on every time then, seems like there should be another way to tell the rest of system to come on! Does anybody know what to do?

 

Correct, 04 xc90 does not require a radio code. A scan with VIDA or equivalent - something that can talk to the ICM might be a good first step.

If a module has a problem these folks do a good job -

https://xemodex.com/us/available-ser...rol-module-p2/