The break wear indicator gives plenty of warning when the pads are wearing down, however it is possible for them to give a false reading. They are just insulated wires that are inserted into the brake pads. when the pad wears down enough the tip of the wire contacts the disk creating a circuit that sets off the warning. When mine started warning, I checked the pads and confirmed that they would go awhile. I just clipped the sensor wire on the most worn down pad which stopped the warning, and ordered the new pads and sensors.

Some have had warnings on nearly new pads. It is not clear whether they re-used an old sensor or had a defective sensor wire, but if the insulation on the sensor wire fails you could get current flowing into the semi-metalic pad which would likely set off a premature warning.

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'97 E 300 D