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01 Silverado ABS Problem
05-27-2013, 10:16 PM
Post: #1
01 Silverado ABS Problem
2001 Chevy Silverado 1500, 4.8L, 4WD, Automatic.

When coming to a stop, at very low speed; 10mph or less, the ABS will activate. You can hear the motor run & feel the pedal pulsing. When this happens the truck wants to go faster rather than stopping. It does eventually catch and stop you but you roll much further than what you would if the brakes just came on normally. This condition is NOT consistent. I drove for over 40 miles; stopping frequently, and only got it to happen may-be a dozen times. I couldn’t find a common factor to making it happen.

I ran DTC’s and didn’t find anything. I test drove while running live data. It has a RF, LF & REAR speed sensors. They are all within 1mph depending on turns where the outside front wheel will run 1mph faster.

I ran an ABS test where you put the truck in Park/Neutral, Key On, Engine Off, Hold the brake pedal down & push the button on the scanner. The ABS motor ran, the pedal pulsed & the test Failed. It said that DTC’s are present. I did a global scan and the only code that I came up with had something to do with the Instrument Cluster? Sorry, I forgot to write it down & now I can’t remember it. I cleared the code & tried several times to run the test again but I couldn’t get the test to repeat???

While running live data I also noticed that the ABS Relay was always “On.” Isn’t that supposed to go off under 15mph?

This truck also had all of the brake links replace not too long ago. I didn’t do the brake lines so I don’t know what all that job entailed. Anything there that might cause this?

I won’t get back to this truck until next weekend. If there are any tests that you want me to run, let me know. Any service bulletins that I should read? Anything else between now & then?

Thanks for using the forum,
Garner

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05-28-2013, 05:59 AM
Post: #2
RE: 01 Silverado ABS Problem
Well guys, I’ll save you the time on this one. I always come here First for the BEST advice. While waiting for a reply I dug into the factory recalls. There was one that described “Exactly” how this truck is acting. It says to remove the Wheel Speed Sensors from the Wheel Bearing mounting hole. Clean the mounting surface on the Bearing, apply dielectric grease & reinstall the sensors.

I should have know this one as I remember doing them a few years back. The recall doesn’t explain “Why” you do this. I don’t think that the sensor has to Ground in the hole? It has 2 wires going to it and it is basically just a small A/C generator. I think I remember someone saying that the corrosion would lift the sensor away from the trigger wheel just enough to mess things up.

So; now that I know HOW to fix it, anybody have any extra input on WHY this fixes it?

Thanks for using the forum,
Garner

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05-28-2013, 10:43 AM (This post was last modified: 05-28-2013 09:31 PM by Rupe.)
Post: #3
RE: 01 Silverado ABS Problem
If that "cleaning" fixes the problem then it was all about a little rust build up holding the sensor away just a tad farther than it's supposed to be. OTOH, I have gone through the cleaning process only to make a minor improvement so I suspect that old age and and temp play a part, what with those flex wires getting frail and possibly the sensor sending a weak signal too. On the last one I did (only a few weeks ago) I tried to replace just the sensor, but me thinks the combination of aftermarket parts combined with 100K miles caused things not to come out perfect. IOW, better but no cigar!

Here's my findings: Sometimes seeing a code in storage but showing as history instead of current. I had intermittent "failing to stop in the normal distance" issues too so I went with my gut feelings. Took a ride in the parking lot over 20 MPH and stepped on the brakes "hands free" to see which way the wheel jerks. It's only for a moment so watch closely. Pulls to the right means the left sensor is dropping out, and pulling to the left means the right sensor is dropping out. When it happens it doesn't always set a fault light. If the light stays on I can find the code as current. (that's what eventually happened)

Some theory: You are right in that the system doesn't work at low speeds, not at first. What goes on there is nothing works in the ABS till you go over 10 MPH then the system is "armed" for an eventual stop. Each time you accelerate over 10 MPH the system arms again. If you stay under 10 MPH (parking lot?) it wil not arm. If one of the sensor signals is not good enough it may not arm till say 20 MPH and if it's out long enough it will trigger the dash light.

Bottom line is that I chased my issue for a few days of normal driving and eventually replaced the entire hub bearing along with a new sensor as I could not tell if it was an OEM or cheesy replacement.... and a "sensor only" repair didn't do the trick, although it seemed better at first.

From experience I can say that the SKF brand replacement hub assembly has Timken bearings and is 40% less than OEM. (still near $300) Most of the other brands have "made in China" or similar stamped somewhere... and they fail early! Also from experience, go to the dealer and buy new bolts to fasten in the hub. The old ones will be rusty and may need heat to get them out. They are in the $6 - $9 range each. You will need 3 of them.

Goood luck!
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05-28-2013, 06:23 PM
Post: #4
RE: 01 Silverado ABS Problem
Thanks Rupe! Very interesting & potentially helpful for when I get back to this one. It might be a couple of weeks, but I’ll post back with what happens for me.

Thanks for using the forum,
Garner

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05-28-2013, 09:46 PM
Post: #5
RE: 01 Silverado ABS Problem
Just an after thought from the above story...

In my case the hub in question turned out to be a cheesy replacement (made in China) so it was a good call that I replaced the entire assembly.

Also from experience, the driver's side seems to fail first. I have seen this on a Yukon, a pick-up, and of course the many Astro vans we still have.

As a side note: I finally have the boss convinced that he needs to replace some vehicles as I now have almost 50% of my Astro vans over 200K with one quickly approaching 300K. In the last year we have purchased 5 Chevy Express vans in AWD but we still have problems to solve. Seems the new vans are only covering company growth. IOW, even though we have all of these new vehicles we have not sold any of the old ones yet because they are all in use. The next problem is the new AWD vans have twice the space but only come in half ton, which means the guys are already over loading them! At one time they were available in 3/4 ton but Chevy discontinued that version because the transfer cases were failing.
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08-28-2013, 09:03 PM
Post: #6
RE: 01 Silverado ABS Problem
Well, I lifted the sensor up until it hit the backing plate, scraped all the rust out from under it, put dielectric grease on the surface & bolted it back down. That was over a month ago & it has worked fine since. I’m going to call that one fixed for now.

Thanks for using the forum,
Garner

Interested in Mining? Look here: Coal Mining, PA
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08-28-2013, 09:15 PM
Post: #7
RE: 01 Silverado ABS Problem
Good to hear you made some progress there.

I forgot to mention that in most cases you can't get the sensor out without removing the dust shield, which is no small task on an older vehicle with rust on everything. If you need to go that far you only have one more bolt to remove plus the axle nut and then the entire bearing comes out.
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