2007 Chevy Suburban service rear park assist message

have it scanned for dtc's,it too hard to diagnose without a code,on these A fault anywhere on the circuit or in any single sensor will affect all of the sensors.these sensors are wired in a series parallel.when testing it should have 8-9 volt reference.its easier to use a scan tool and switch sensors with different locations and see if the dtc sets on a different location,post back with the code.