I own a 2002 Jetta TDI and the brakes have been troublesome since purchase. At times it feels like the brakes are slightly engaged and will disengage only after coming to a full stop and pressing the pedal to the floor. At this point I can smell the odor of brake pad. The dealer looked at it a year ago but found no evidence of abnormal wear. The problem continues and this weekend while driving and I heard a high frequency squeel and when I applied the brake a loud pop of air came up out of the brake pedal and the pedal went spongy. I travelled a 1/4 mile, braked again and the same thing happened (very scary). Got the car home using the emergency brake and the brake light stayed lit after parked. Had it towed to the dealer and he, of course, says they can find no sign of a problem and can't get the issue to occur while driving.
Does anybody have a clue what is going on here? Thank you for reading this.