I'm going to park my Lexus for three weeks, what do i need to do?
If it were me, and the car was locked in a secure garage, I would just park it. When you get back to it just put a charge on the battery before starting.
Fill up the gas tank to avoid condensation problems but three weeks is really not a long time. If it were three months I would add a fuel stabilizer to the gas and disconnect the battery or put a battery tender on it.
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