99 Sierra ABS issue

I have a 99 GMC Sierra (new body)w/25K miles, when I am braking at slower speeds(under 5mph), the ABS comes on, the ABS light does not come on. I took it to the dealer and they told me I needed four new
rotors. For a $1000.00 they said they would try this to see if it works. So I decied to do this myself. I pulled the front rotors, they were indeed rusty, Pep Boys wouldn't touch them so I ordered new ones and will put them on this weekend. I will try the front rotors first, see if this fixes it.
When I looked at my reciept from the dealer, I noticed that the tech who read the codes said the L/F sensor was open...The dealer did not mection this as a fix.
After reading several post, for older body trucks, it mentioned that cleaning the ABS sensor area would fix this problem 95% of the time. Is this true for new body trucks as well? I noticed the sensor seems to be mounted in a hole that is drilled into the bearing housing, seems easy enough to clean.
Any thoughts?
Thanks
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"Fred Reyes" wrote

This will probably fix your problem. You need to clean the surface of the bearing housing where the sensor attaches to it. What happens is that the rust and corrosion will actually push the sensor away from the reluctor and you will get a "dropping out" of the sensor signal at low speeds. This translates into ABS activation as the computer "thinks" that it is seeing an ABS event. No ABS diagnostic light will appear as it's perfectly normal for the ABS to see one wheel "lockup" under low traction conditions. It just doesn't know that it's "not" a low traction condition....but a sensor problem.
Replacing the rotors won't have anything to do with this problem. Other then make somebody a little richer.
Ian
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Good advice as usual Ian, around here the shop I help out p/t in, is the only one aroud that is doing this rather than replace the bearing ass'y.

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"David J and Lynne J Shepherd" wrote

Well...I will admit that when we first encountered the problem, we just replaced the bearing assembly until we figured out what was going on. If I recall correctly....at that particular time, you couldn't get the sensors separately from the bearing assembly, even though it was very obvious from looking at it, that it could be removed. Eventually, GM released the sensor separately and a bulletin outlining the rust problem. I've noticed that all the late model versions of these sensor/bearing assemblies now use a small stainless steel plate as the surface that the sensor sits on. Obviously an attempt to keep corrosion problems down around the sensor area.....and it seems to be working, as these problems have dropped off lately.
Ian
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Sure if the sensor is pushed away from the interruptor (tone wheel) the air gap is large enough to cause the sensor to run out of range.
Have a great one!
Bush
Discourage inbreeding, ban country music.
On Wed, 12 Nov 2003 06:26:59 GMT, "shiden_kai"

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Ian,
Thanks for your input. I saw an older post that you did and I just wanted to make sure the same fix for Sensor/Hub can be used on the new body pick-up as well.
Whats's the deal with the rotors on this truck. Although it isn't the cause on the ABS problem, they sure are rusty, in fact the surface flaked on one of them! I haven't ever seen rust on rotors like this before. Its only a 99 w/25K miles. It wasn't used for a month, but this is crazy!
Thnaks Again,
Fred

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"Fred Reyes" wrote

About all that you can do is take the sensor off and see if you do have a buildup of corrosion. It will be a trial and error procedure basically.
> Whats's the deal with the rotors on this truck. Although it isn't the

Yep, I've noticed that the new style trucks do have issues with the rotors rusting. The brake pads on these trucks, (especially the front pads) last forever, and you actually begin to have corrosion/sticking problems with the pads long before they wear out. I've done a number of brake jobs on these trucks where the rotors were badly rusted and the shoes, although they had plenty of meat left, had badly grooved and rutted surfaces from the rotor.
Probably GM saving some money and using cheap rotors.
Ian
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Ian,
Thanks for your input. I saw an older post that you did and I just wanted to make sure the same fix for Sensor/Hub can be used on the new body pick-up as well.
Whats's the deal with the rotors on this truck. Although it isn't the cause on the ABS problem, they sure are rusty, in fact the surface flaked on one of them! I haven't ever seen rust on rotors like this before. Its only a 99 w/25K miles. It wasn't used for a month, but this is crazy!
Thnaks Again,
Fred

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Ian,
Its like magic, your suggestion worked....I broke the first sensor, but the second I took out and cleaned-up.
Thanks,
Fred
snipped-for-privacy@att.net (Fred Reyes) wrote in message

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"Fred Reyes" wrote

You are welcome, Fred...glad it worked out for you.
Ian
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