I have had this problem twice. Once 10 days after delivery & again at 8 months. In both cases it was a bad sensor....3 days to fix each time (part delivery.) It was drivable but very rough & bouncy.

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2008 4.8i Mineral Green Metallic Sports Package, Technology Package, Cold Weather Package, Rear Climate Package, Premium Package, Premium Sound with iPod adaptor & Sirius Radio, Auto Tailgate, Head up display