Reverse Converter Control
WARNING: This page is about a different car, the 2011 Lincoln MKZ and 2011 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
If the selector lever is moved from N to R while the vehicle is moving forward and the transaxle shifts into REVERSE, the wheels will be locked, which is extremely dangerous. In order to avoid this, the TCM inhibits the transaxle from shifting into REVERSE while moving forward.