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ABS Pulsing on Dry Pavement


tblake
11-21-2010, 12:23 PM
1997 Chev k1500 4x4

When I first got it over a year ago, it maybe pulsed the ABS once in a year on dry pavement. I attributed that to maybe having some sand. Within the past month, the truck has been randomly pulsing the ABS system when using the brake at speeds lower than 10mph. You can feel the pedal get firm and hear the ABS motor run. The ABS light is not on.

I really should get this fixed before we have get snow again. It sounds like a bad wheel speed sensor, or bad wiring to me. I have no scan tool capable of watching wheel speed sensors.

I see I can buy the front sensors minus the hubs with new wire for about 50 bucks each. Which is what I might do. I would just like verify which sensor/wiring is giving the issue before I replace anything. I guess I have a 50/50 chance of replacing the right one. So not terrible odds.

Is there a way to test them? What is the ohm spec on the sensors? Its going to be tough Iím sure because its an intermittent issue. Are there speed sensors for the rear wheels too, or is that signal off the VSS sensor in the trans?

I just donít want my g/f to be driving it and lose ABS on a snowy road.

Thanks.

Blue Bowtie
11-21-2010, 02:15 PM
A typical Hayes wheel speed sensor should read between 600-1,400 ohms through the pickup coil. The sensor should produce between 0.2-0.8VAC when the wheel is turned at about 60 RPM (one revolution per second). You should test this not only at the wheel speed sensor connector close to the wheel but at the EBCM connector to make sure the harness and connections are in good condition.

As an aside, recent NHTSA tests have reportedly substantiated the test results from Bosch and Mercedes-Benz that ABS systems actually increase stopping distance in marginal traction conditions. This has been kept very quiet, since the NHTSA and insurance companies really don't want you to know about that. In short, losing the ABS might not be a bad thing, and could force drivers to actually use skills instead of reaction when operating a vehicle. It used to work that way.

j cAT
11-22-2010, 09:55 AM
this issue of abs activation at low speeds may mean the hub bearing is going or rust has caused the voltage output to drop too low at the slower speeds.. remove sensors if hub grease has rust the hub is bad, also clean sensors off and the mounting surface of the hub...

abs activation can occur because of road defects..especially at low speeds...too much air in the tires ..........

using an ac voltmeter you should get over 300MV AC when rotating the hub at the sensor connector.....

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