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 ETACS-ECU and the power liftgate control unit, the ETACS-ECU itself or the power liftgate control unit itself may be defective.