Welcome to the world of the XC90 and this forum.
Unless any problem is obviously mechanical, the only way to know what is going on with the XC90 (and most other modern cars) is to get into the computers that run it. That means using a scan tool (or scanner) to read the DTC's (diagnostic trouble codes) and see what is going on in there. For Volvos the only scanner worth using is their own VIDA/DiCE system.
It used to be that only dealers and specialists could afford this system but now you can have one for about £80. The software (VIDA) runs on Windows 7 Pro and the hardware interface (DiCE) is knocked off in China and sold on eBay etc.
Most issues will be much easier to fix with VIDA. It can interogate all the modules and give real diagnostic data. Simon (CheshireD5), on this forum, will sell you a complete system on a laptop.
Which is all a long way of saying you may have a problem with the module in the stalk. VIDA will help or you could just remove it and give the contacts a clean for starters.
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Greg
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