elliottwicker

I have an 04 F150 STX 2wd, 4.6L, auto, 77,000 miles. During braking, and just before the truck comes to a full stop, the brakes start pulsating like the ABS is detecting a skid. The pedal gets hard and braking effectiveness is reduced. Sometimes the ABS light comes on, but resets when I turn the key off. Brakes seem to work normally at all other speeds...this only happens at very low speed. I can pull the ABS fuse disabling the system and the problem goes away, but I lose ABS and the yellow ABS caution light stays on.

DORMAN68

I have ran into this issue on my buddy's Silverado. Sounds like a bad wheel speed sensor and or tone ring on the axles. I would check the tone rings for cracks and or debris and make sure the sensors are fully seated. Sometimes rust or dirt builds up behind the wheel speed sensors causing them to lift up just enough where the sensor can't detect the rotation of the axle/tone ring. Just a thought, hope this helps.

elliottwicker

I think GM had issued an AD for this problem on the Silverado. I checked for this on my truck - even removed and reinstalled the speed sensors - but no change. My problem seemed to start shortly after I had to replace the front rotors (didn't use OEM rotors...too pricey). I didn't notice any cracks when I bought them and they looked identical to OEM, but maybe the tone rings weren't built and/or installed to factory specs.

Anyone know the gap specs between the tone ring and sensor? If the rings and sensors are in good shape, but the gap is off, would that cause the ABS to fail only at slow speed?