The sensors get hard and brittle over time from the heat. If he didn't replace the rear sensor, he still had to have it out to change the pads, and it is the most likely reason for the light being on. As mentioned above, no reset necessary if the sensors are hooked up and functioning correctly.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue