Backing up my sensors work , flawless operation , however when I press the rss off switch in the radio center panel to silence it it won't silence, the "off" light does NOT illuminate , the audible sound stays on. Had the switch checked at ford they used a volt meter and said it was functional and wouldn't help me further without starting a work order. This problem suddenly stopped working last season and I'm stumped. My thoughts that if it's a sensor in the bumper the audible would not be functional and if it was the switch they would have seen it with the voltmeter , I don't want to take it in. please any ideas

 

Oh yea 2005 f150