Rear Access Door Open Warning

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Receive warning that the Rear Access Door is Open. Can't find a sensor near the door for this alert. Confirmed hatch and door are fully closed and secure. Of course with it thinking the door is open, the dome lights stay on while driving but do turn off with delay when engine off. Problem has been consistent for 1 week now. Mileage is 110,000. Where do I look to troubleshoot the problem?