The dealer "tops off" my DEF at oil change, which is usually 7K-8K ( the computer decides). The tank doesn't come close to running dry, and usually takes a couple of gallons. No big deal. You can also buy DEF anywhere from a truck stop to a WalMart. Your screen lets you do a scan to make sure your DEF isn't low, and you will also get a warning on your screen if it drops below a certain level.
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