Removing the bumpercover just behind the license plate will reveal a hole large enough to get the sensor out from the bumper...the rest of the looming process is a little trickier.

As I stated earlier from experience, it's usually the dash indicator that goes bad, not the sensor wire...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car