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Reverse sensors Fixed - easy trick they don't want you to know about.
I sanded my reverse sensors with 1000 grit sandpaper and no more long beep at first reverse shift.
that is the short story. I polished and waxed my S and for the next few days I noticed that the reverse beep was gone. That got me thinking, "what if?" So I had some 1,000 grit sandpaper nearby (500 grit would be fine also) and taped off the surrounding area then proceed to sand away some clear coat. After a few quick tests, nothing changed so I kept sanding, kinda broke through the clear coat and figured I would stop there. On the next few tests it was still beeping so I figured it was a fantasy and wasn't going to work. I peeled the tape off and got ready for work and on the next start up and ever since No more long beeeep when put in reverse! YRMV but its cheap, easy, worth a try and alot easier than pulling the bumper and replacing sensors )
Last edited by RLucky82; Jun 26, 2019 at 07:48 AM.
Sweet, I'm going to give it a try. I bought my R52 used last year, and it had the long beep on reverse. With the help of my son (young ears) I determined which of the four transducers was not sounding. Then I bought a couple of sub $20 generic black transducers from different suppliers and swapped it out with the first to arrive.
The long beep went away, but the system doesn't function... I've never heard it beep as I back up close to things.
I haven't yet tried swapping it for the second cheap one. I think OEM paint matched sensors are about $280 each.
Mine got water in the sensors in my R52, pretty typical behind the seal. Then you set it out in the sun and let dry out and its works. Once i drive it through the ran or wash it really good it comes back.
Watch on those high-pressure hoes as it can force water in there and cause the sensor to have a long beep again.
Put the car in reverse and of course on but not running, put your ear up to the sensor and you can hear it ticking, If no ticking you know which sensor is bad.
Put the car in reverse and of course on but not running, put your ear up to the sensor and you can hear it ticking, If no ticking you know which sensor is bad.
My ears are old and I've had a bunch of ear surgeries. My hearing is nearly normal for my age, but I couldn't hear anything from any of them. My 17 year old son had no issues telling which one was not ticking.
Note: you can do this test with the engine off but key on, so no danger to the person squatting down behind the car which is in reverse.
Sensor has a little seal on it , i thought the same thing but i did not damage that seal as thats how water gets in there and ruins the sensor. I have seen people just switch to the black/non painted ones we have, but then you can see those black dots on the bumper.
YRMV but its cheap, easy, worth a try and alot easier than pulling the bumper and replacing sensors 
