ABS false activation

[joshuacain]

I own a 97 GMC Sierra Z71, and I've been experiencing false activation of the ABS when coming to slow controlled stops under about 5mph. I've been reading up on this problem and have discovered that the speed sensors on the hub wheel bearing assemblies have developed some corrosion between the assembly and the sensor. This causes the sensor to raise up slightly cause the air gap to increase between the magnet on the sensor and the teeth inside the wheel bearing assembly. This causes a decrease in the voltage generated by the metal teeth passing accross the sensor magnet. The voltage generated should be no less that 350 mV. When the voltage drops below this voltage the ABS engages. The way you test the sensor is to disconnect the sensor cable which is inside the wheel well about eye level if your on your knees. After you've disconnected the sensor wiring plug, insert the red lead of the multi meter in one side of the plug and the black lead in the opposite side of the plug. Then rotate the tire at hand speed and observe the voltage induced. You should only have to spint he wheel maybe 2 revolutions at a fairly slow speed to induce 350 mV. If you have to really break a sweat turning that wheel then you know one of two things. Either your speed sensor has failed and needs to be replaced or you need to remove the sensor and take some emery cloth or a fined file and remove all corrosion from the mating surface. Once the corrosion has been removed and the surface is shiny metal, replace the sensor and repeat the test. Be carful not to remove much metal from the surface of the wheel bearing assembly, only whats needed to remove the corrosion. This is what I found fixed my ABS problem. I hope this is helpful.

Joshuacain