MickeysPal — The Toyota-marketed "Park Assist" system, also known as "Park Pilot," uses four backup sensors, and its electronic control module requires all four. Other systems might use different numbers of sensors. It's also possible that the sensors' characteristics are specific to the individual systems. If so, don't combine sensors from manufacturer A with electronics from manufacturer B unless you know that they will work properly together. My Park Pilot was installed by the dealer before delivery. I don't know the manufacturer's name. I don't think it was on either the Owner's leaflet or the Installation Instructions. See my posts in the thread "Park Assist ATTN: Droid13."

Stan