I had same issue as well cause of ice and snow. Once i cleaned all ice off and out of the groove of sensor it's all good.

 

Common issue when it gets cold/snowy/icy... Will more than likely go away when it thaws out.

 

Just adding that mine do this too in the cold weather. Works normally again when the temps warm up. Cleaning them makes no difference in my case.

 

To add a troubleshooting step, mine did this and the sensors themselves were clean. I reached under the bumper and found the wire running the sensor (it's very obvious) and just moved it around a bit. A lot of ice and crud broke up and the sensor immediately stopped going off.

It still works, before someone says I broke it. It just works correctly. Haven't had a problem since.

It did it on my two outboard sensors right after we had an unusual heat wave and then rapid freeze overnight. My guess is my tires kicked up a bunch of rain into the wire/connector and then it froze.