Comments On Trouble Symptom
WARNING: This page is about a different car, the 2014 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.
The wiring harness or its connector(s) between the power liftgate close switch and the power liftgate control unit, the power liftgate close switch itself or the power liftgate control unit itself may be defective.