You have to pull codes to determine the exact cause and diagnosis. A technician can do that.
Off-hand, the most common cause of this light coming on is a defective brake light switch.
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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
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