2008 XC70 Parking Sensors

[jrbuzz8]

Hello!

I have had an error message in my 2008 XC70 for a while regarding the parking system. It tells me every time it starts up, "Park Assist System Service Required," so I finally decided to go ahead and replace all four rear sensors. After doing that, the error message still shows up. I am unable to identify which ones are not functioning correctly because the car totally disables the system when it finds a fault. How can I figure out where the problem is? I am mildly annoyed that I spent the time and money to replace the sensors and nothing changed. I figured it might be the sensors, as when they get wet, the error message does not immediately appear upon starting the car like it normally does. The new sensors are all clean and clear, and I properly painted the middle ones to match the rear bumper. Is there a definitive way to figure out what the problem spot is or do you just keep replacing parts in this system until it is fixed? Thanks!