Quote:
Originally Posted by tangofox007
What's it going to tell him that he doesn't already know?
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Sorry.. didn't followup with the thread.
Don't know MB specifically, but on every car I've ever worked on, the brake system was divided into two zones that each consisted of opposite corners of the car. Among other things, the sensor that lights the light checks that both zones have equal pressure.
So.. if one zone leaks, there should be a difference in pressure and the light should illuminate every time you press the brake pedal. It is a useful diagnostic if you suspect a leak, but it can fail too, the most common failure being that the indicator bulb burns out.