I had an intermittant yellow and red light in my 300SD. Fluid was fine, pad thickness was fine. Sensor was faulty...shorting out...esp when raining. I tried electrical tape but still happened. Sensors are ~$10 for 4 plus shipping.

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1983 300SD 307k miles
1993 Ford Escort Wagon 215k miles
1995 Isuzu P'up 214k miles