ABS sensor repair, replace, options? - PeachParts Mercedes-Benz Forum

stephenson · #1 01-07-2013, 10:50 PM

The description in this thread seems consistent with what I am experiencing ...

85 300SD - Brakes - ABS noise/softish pedal?

I'll do the tone ring cleaning on RF sensor ... the sensor checked OK in resistance test ...but the 8.15 VDC expecting 4 VDC is still the only thing I can consistently point to as likely cause factor.

stephenson · #2 01-08-2013, 06:56 PM

Well, today things got better .... finally.

Today I removed the RF wheel sensor, and carefully examined it, the wiring from the sensor to the grommet at the wheel liner, the knuckle where the sensor is attached, and the tone ring. Not finding anything unusual, I carefully cleaned the sensor, sanded the outside of it lightly with very fine sandpaper, including between the two tips on the end of the sensor, sanded the base plate where the sensor attaches, sanded the inside of the sensor mounting plate, sanded the inside of the sensor receiving tunnel, carefully cleaned around the base of the tip of the sensor with a small tipped awl, inserted the awl through the access tunnel and used the tip to clean every tooth in the tone ring, then sprayed everything with brake cleaner, using compressed air to completely remove any disturbed material.

I then tested the output of the RF wheel sensor and found it, again, to be 8.15 VDC with ignition on, but when spinning the wheel at 1/s it now at 4 VDC (the spec number)! The LF wheel always tested 4 VDC with wheel spinning, but always tested at zero (0) when the wheel was not spinning.

Put it all back together and everything worked per spec – the ASD triangular light illuminated during start sequence, the ABS did no actuate during stops, the ASD triangular light illuminated when I accelerated and spun the wheels on a gravel/dirt road and then went out per spec.

A good exercise in troubleshooting!