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I don't know the exact job but it tells the computer the position of the rotating camshaft. They are know for failing. Most of us carry one with us for when they do, also they are extremely expensive from the dealer, a little cheaper from international, and 60 bucks shipped in a ford oem sealed plastic bag from ebay. So when it goes bad and have a spare you don't have to get one from the dealer to get your truck up and running right away.