I have had three rounds of a parking sensor go bad over the years. Same long beep. The codes always have the wrong location, so I don't even try anymore. Have someone trustworthy start the car and put it into reverse to engage it. Walk around with your ear close to each sensor. Working sensors make a very faint clicking sound. I can also feel it if I touch the sensor very lightly when it is operating. Was always just one for me... Used sensors can be found cheaply on eBay.

__________________
David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles