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[RedRocket]

Please remember that at least one sensor is broken:
"with front system used with rear sensors: when connected to rear sensors,no error message but only one sensor works as parking sensor. But both detect my laser tester."

Ok, we can use this, but don't use the Laser Tester,the output is to wide & not useful to draw conclusions for which sensor or cable is the bad one.

Use your hand instead- by placing it close (about 10mm) to each one, see if you get U-boat "ping" sound from each Rear sensor.