If one sensor is dead the whole system will not work! I have pre fl and I can take out sensors out from front bumper! As far as I know for fl cars u have to take off the front bumper! But I can be wrong! There is no problem about rear bumper! I had sensor pushed in in to the rear bumper and whole system was sounding in reverse! I took it out and no problem! I had problem only few times with my sensors as I mentioned...during winter or after washing! I walked around car checked sensor with hand and cleaned sensor with some cleaner