Call Diana in service she is unreal.
Idk about exact pricing, but the CD's you can buy that upgrade the maps are like $125 or $150. Thats the only upgrade unless youre talking about completely upgrading your entire system.
An actual upgrade or update? With an update they can only charge labor since they are free on cadillac's website and upgrade may be difficult since your car is older then the more modern system they use today.
Not sure, you'd have to call the dealer. I'm pretty sure they have something available though
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