From Dictionary.com, uninstall is a word, but uninstallation is not. I tried deinstallation and that isn't a word as well. Is there any word equivalent, ending in -tion that is a real word?
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I think a good antonym for "installation" is "removal". It doesn't end in -tion, but it is a clear word which refers to taking something out. (On the other hand, installing is putting something in.)
Interestingly, uninstall is only used in a computer science context.
Since you want a word which ends in -tion, how about extraction?
First you install an immobiliser. If the unit is faulty, you could extract the immobiliser for repair or replacement.