I have an 'fSport' which was delivered in September 2012. I thought I was getting factory fitted sensors and I paid the price quoted for them. When I took delivery, the very same day, it was clear to me the sensors were not working as they should. They sounded off almost continuously at the slightest thing, including approaching traffic on the opposite side of the road, both front and back, and very loudly. After an hour or two driving, when they were driving me crazy, I went back to the dealer, that same day, and complained. Initially the dealer claimed there was nothing wrong other than them needing the volume reducing. I pointed out that they were constantly sounding and therefore not only a distraction, but useless in a car park, thus defeating the object of having sensors.
The dealer eventually found a deactivation switch for the front sensors (hidden beneath the dashboard) and reconnected the rear ones so that they were only active in reverse gear. I insisted that they move the switch into the bank of switches and reduce the volume. In all I was there several hours on the first day when I took delivery while they got it sorted; not a good experience with a new car! Even after that I was not happy with the sensors. After some bitter argument with the dealership manager, when he admitted the sensors were not factory fitted, and probably fitted by some trainee mechanic who hadn't got a clue, I got my money back (£560 I think), but I am still far from happy with the sensors. The rear ones now sound constantly when I engage reverse and I never switch the front ones on. I will have them removed at the first service.
In summary my view is that they are cheap sensors fitted by the dealer out for a quick profit. Even the tinny sound of them is cheap, not up to Lexus standards and I am embarrassed when I have passengers in the car. I am delighted with the car itself but my dealership experience is shoddy to say the least.
SM