Reverse Converter Control
WARNING: This page is about a different car, the 2006 Mercury Milan, 2006 Lincoln Zephyr, and 2006 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
If the shift 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.