Just had my rear parking sensors replaced. I bought these on Amazon for $15 each. They all seem to work. I start up the car, turn the sensor function back ON and got no fault message, a good sign. I placed the car in reverse and had my wife walked toward each of the four sensors one at a time, they all work. The problem is when I back the car up on a level street, the inner sensors are beeping with no one behind the car. All the sensors read 10k ohm, I had no fault message and they all functioned independently with a person walking toward them. Is there a correct orientation they should be mounted to the car? I put them on with the plug connector facing the wire hardness connector. Are the sensor reading the ground or the pavement?