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ABS Activates at Brake Application 2003 3500 Exp

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Old June 18th, 2021, 10:52 AM
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Default ABS Activates at Brake Application 2003 3500 Exp

I just bought this and I could hear a motor actuate when stopping.
I assumed it was motorized power brakes.
After driving it more, I can hear/feel the ABS operating, and a pull to the Pass side.
4 w disc 9800 GVW

Prev owner says it's murder in Winter. Yeah ...

I really don't know where to start looking, I'd do a visual, but I'm not sure what I'd look at besides verif the components are actually there
So any pointers on where to start I'd appreciate it.

Thanks in advance
Old June 18th, 2021, 11:49 AM
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it's usually worn wheel bearings
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Old June 18th, 2021, 12:15 PM
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Thanks!
These are a sealed cartridge?
368k on chassis ...
Old June 18th, 2021, 4:04 PM
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hub assembly then
Old June 18th, 2021, 11:46 PM
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Originally Posted by Uptownsport
I just bought this and I could hear a motor actuate when stopping.
I assumed it was motorized power brakes.
After driving it more, I can hear/feel the ABS operating, and a pull to the Pass side.
4 w disc 9800 GVW

Prev owner says it's murder in Winter. Yeah ...

I really don't know where to start looking, I'd do a visual, but I'm not sure what I'd look at besides verif the components are actually there
So any pointers on where to start I'd appreciate it.

Thanks in advance
false abs activation can occur when a wheel speed sensor signal drops out. The symptom is: when braking at slow speeds the abs pump comes on and the pedal goes deep to the floor with little or no stopping power. no codes set in the ebcm. the signal drop out makes the ebcm think a wheel is locking up; so it opens the abs dump valve and releases brake line pressure to that wheel.

this was very common on systems using passive wheel speed sensors. 2003 uses passive sensors.
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Old June 18th, 2021, 11:50 PM
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yes I remember very distinctly my 2000 Astro doing just that. It got me into trouble because ABS would actually increase stopping distance.
Replacing the hub assembly resolved the issue.
The active sensors on my 2013 Savana are much more reliable.

Last edited by mountainmanjoe; June 18th, 2021 at 11:55 PM.
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Old June 19th, 2021, 10:23 AM
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Originally Posted by tech2
false abs activation can occur when a wheel speed sensor signal drops out.
Originally Posted by mountainmanjoe
yes I remember very distinctly my 2000 Astro doing just that.
Yep, you both described it as if you were behind the wheel.

Not wanting to replace a hub cartridge because of a little sensor if i can help it. RA lists sensors for front.

Logic: Pulls right, bad left?

Thanks again, gents.
Old June 19th, 2021, 10:41 AM
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rust forms and pushes the sensor away from the tone wheel. this causes the signal fall out at low speeds as the signal is weaker the slower the reluctor rotates. to find out which one is bad....remove the sensor from the hub....any that are stuck and will not come out are the problem. once you have them out....remove all rust from the hub mounting surface and bore. install new wheel speed sensors into the hub. the wss should be approx $40
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Old June 19th, 2021, 11:43 AM
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Yup rust will do it.
I suggested bearing because you said your van also pulls to the side. And I think that a sloppy bearing also affects the ABS sensor gap. It's easy enough to test. Just jack up the vehicle and wiggle the wheel around.
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Old June 19th, 2021, 10:52 PM
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Thanks. It pulls because of the ABS. Otherwise it seems to go down the road and stops fairly straight until ABS kicks on.
Pedal went to the floor at the stop on the way to the shop. Drv's Rr caliper is wet- Dunno if hose fitting is leaking or?
I've never seen a caliper leak in my life.
The Wheels studs where literally the tightest thing I've ever loosened. I broke a Snap On 1/2" Breaker and needed to put a 7' pipe on the 3/4" for leverage.

So all the other fixing is going to make it take a while to get to the ABS sensors.
It says how big a wreck it is when the brakes aren't even on the top of the list of things to fix!!


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