Code No. C1621: Electronic controlled coupling solenoid (center) protection: Operation
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 AWD-ECU calculates the electronic control coupling temperature by the information of the electronic control coupling control amount, outside temperate, etc. If it is detected that the electronic control coupling temperature becomes extremely high, the high fluid temperature warning is displayed on the warning indicator.