Retired Ford Powertrain senior leader here. The failure, which Ford prefers to blame on suppliers for financial liability reasons, is generally due to a shortfall in the preparation of a document called a DFMEA (design failure mode effects analysis). The document, while not easy to write, provokes the system or sub-system engineer to forecast what will happen if, in this case, the electrical signal between the engine control module and the vehicle speed sensor is corrupted. This loss of communication makes the engine think the vehicle is stopped and shifts the transmission into first gear. The reasons for the “loss of signal” are many, some known and some unknown. If it was foreseeable and action wasn’t taken to correct it, well….., that’s what punitive damages are all about. On safety critical systems, conductive grease, gold plated terminals, etc. are used. One last memory, push together electrical connections and good for 5-6 connects, before the electrical resistance increases….fast.
Tom H.