One problem related to brake sensor has been reported for the 2007 Mercedes Benz GL450. The most recently reported issues are listed below.
2007 Mercedes Benz Gl450, did all scheduled maintenance at dealer, only 36000 miles, the 'brake wear' message just came up on the console. Dealer checked and said all brake pads, front brake rotors need to be replaced. So only 36k miles and well maintained vehicle, when the brake sensor just indicated 'brake wear' problem, not only all pads are bad, but also the rotors were damaged already? it seems to be defect of brake system, including the brake sensor.