Brake Problem, ABS kicking in?

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KennethO
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Brake Problem, ABS kicking in?

Postby KennethO » Sun Sep 11, 2011 5:54 pm

Randomly when stoping from a slow speed of about 5-10 mph. The brakes stop, then release and then catch again. Its almost like if you were stoping on ice and sliding a little. During this you can hear clicking in the driver side of the engine bay that sounds like relays. This makes me think its an ABS problem.

Faulty or dirty wheel speed sensor? How do you clean them? Brake cleaner and a rag?
Anything else that might cause this?

Thanks, Kenneth.



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Re: Brake Problem, ABS kicking in?

Postby DTMAce » Mon Sep 12, 2011 12:45 am

I would check the sensor's gear, make sure you have no missing teeth. Front ones are easy to check, rear ones are not.

Next I would reseat each sensor connector, make sure they are all plugged in good. May have a bad sensor.

Dirt? Not likely. The sensor works by electromagnetism. In short, the sensor picks up or generates a pulse/signal each time one of the metal teeth pass it. SO. Dirt and stuff really don't affect the way the sensor works, however dirt and that can corrode or cause issues with the wiring/connector, causing misreads of the unit that way. One reason I suggest unplugging and reconnecting the connectors. May want to make sure they are clean, etc.

Most problems are going to be the front sensors. The rear's are enclosed inside the bearing and connected inside the axle so are less prone to problems, but if you ever replace the rear bearings, you get new sensors with them. Or you should anyway. lol

Obviously, you can make sure its the ABS that is causing the condition by disabling it. Just pull the fuse for it, see if the problem goes away at least.

The brain box for it could be bad as well I suppose. Mine went bad the very first winter I drove the car (94). It acted up, started only anti-locking the driver's side wheels, I nearly lost control and slid into a ditch, but was smart enough to manually anti lock myself, and once the ABS light came on, that problem went away and it at least worked like a car without ABS. Dealership replaced the whole brain/control module for it. Haven't had an issue since.

Good luck.


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Re: Brake Problem, ABS kicking in?

Postby Chad91GTZ » Mon Sep 12, 2011 5:57 pm

Dirt no, brake dust, YES.

Especially because of semi metallic brake pads. Wipe them down with a clean rag, they are magnetic obviously so it will take a few tries.


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Re: Brake Problem, ABS kicking in?

Postby SuzukiGhostRider » Mon Sep 12, 2011 6:08 pm

I really wouldn't suggest brake cleaner to clean ABS sensors.


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Re: Brake Problem, ABS kicking in?

Postby Chad91GTZ » Mon Sep 12, 2011 6:10 pm

SuzukiGhostRider wrote:I really wouldn't suggest brake cleaner to clean ABS sensors.

Exactly, especially not chlorinated brake cleaner. It has this habit of eating plastic.

Brake cleaner is for drums and rotors, not your windshield, not your headlights, not your tires, and not your hands. LOL


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Re: Brake Problem, ABS kicking in?

Postby SuzukiGhostRider » Mon Sep 12, 2011 6:18 pm

Exactly. :D


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Re: Brake Problem, ABS kicking in?

Postby DTMAce » Tue Sep 13, 2011 12:12 am

Chad91GTZ wrote:Dirt no, brake dust, YES.

Especially because of semi metallic brake pads. Wipe them down with a clean rag, they are magnetic obviously so it will take a few tries.


Apparently I don't get this comment.

Mostly because the ABS systems I'm familiar with work the following way:

The metal teeth on the "gear" pass through/by a set of encapsulated coil windings in the sensor. So when a ferrite based metal (such as iron or steel) passes near a coil of wire, it generates an small electrical change/charge in that wire. Depending on how the ABS is designed, there typically should be nothing overly magnetic that would cause any iron particles to accumulate.

Now, it is possible the the ABS system generates an electromagnetic field while the ABS system is active, and it simply monitors the sensors for change within that field to detect the "teeth" as they pass near the sensor. But this should still be a weak enough field to again not attract that much magnetic material. Or light enough that a good wash should remove them quite easily. especially if the ABS system is powered down. (as when the car was not running)

When the sensors are having trouble, they usually only screw up when teeth are missing or have a bad wiring connection. I had the teeth problem on the older caravan. Both front wheel axles had a couple of teeth on EACH gear missing. So at low speeds, when I would brake normally, the van would try to anti-lock me. I would have to release then re-brake to get it to stop finally.

Once I replaced those axles, never had trouble again. And it worked better on conditions that warranted the need for anti-lock brakes. Sadly the 03 Caravan I now own does NOT have anti-brakes at all. Not even installed.

Anyways. I may be wrong and that's ok, this is just my understanding of how they work in most applications. They designed them to work this way, to provide less issues with reliability or failures resulting from things like dirt and brake dust. Ah well.


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Re: Brake Problem, ABS kicking in?

Postby Chad91GTZ » Tue Sep 13, 2011 12:27 am

There is a magnet in the wheel speed sensor. it doesn't shut on and off. its just a magnet.


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Re: Brake Problem, ABS kicking in?

Postby scd88ga » Tue Sep 13, 2011 2:27 am

Chad91GTZ wrote:There is a magnet in the wheel speed sensor. it doesn't shut on and off. its just a magnet.


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Re: Brake Problem, ABS kicking in?

Postby DTMAce » Tue Sep 13, 2011 2:52 am

lol

Ok, so I was mistaken. Not the first time! Still makes no sense to me why they would need actual magnets in them, but whatever works! Apparently its a passive design, lets the proximity of each metal tooth change the field strength of the magnet, causing the sensor to pick it up that way with its wire loop. AH well. Would make for a stronger spike in the sensor, easier to detect, but it would have worked with an active design just as well.
Yeah that will collect every particle of ferrite metal it encounters. And that can have an effect on the field strength of the magnet, which could affect how well the sensor's resolution works. But I would think that would affect it more at higher speeds, not lower speeds.

I would check the teeth, make sure all of them are there on both front axles. Clean the sensor if its badly covered in metal debris, and re-seat the connectors for the sensors.

Good luck!


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Re: Brake Problem, ABS kicking in?

Postby 3X00-Modified » Tue Sep 13, 2011 8:24 am

Its a hall effect sensor... so yeah it's a magnet, or at least has been turned into one...

Honestly I wonder after they are built and not used yet if they are magnets, because I know they still send a electrical voltage to the sensor to energize it to a certain level so it can detect the presence of the toothed reluctor gear passing by.

My theory is it's like an electromagnetic nail... Wrap wire around it and it will become a magnet, remove the wire and it still has some of those magnetic properties, just not as strong.



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Re: Brake Problem, ABS kicking in?

Postby Chad91GTZ » Tue Sep 13, 2011 12:16 pm

It is a permanent magnet, with a coil wrapped around it. When the ring gear passes by it changes the magnetic field it generates and induces an AC current. Like a generator. That voltage level is sensed by the ABS computer.

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Re: Brake Problem, ABS kicking in?

Postby KennethO » Tue Sep 13, 2011 12:28 pm

Took off the sensors and gave them a good cleaning. They did have a ton of metal particles on them. About 1mm thick. Also took a brush and cleaned between the gear teeth incase there might have been anything stuck between them. Seems to be working fine now.



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Re: Brake Problem, ABS kicking in?

Postby 3X00-Modified » Tue Sep 13, 2011 1:08 pm

Chad91GTZ wrote:It is a permanent magnet, with a coil wrapped around it. When the ring gear passes by it changes the magnetic field it generates and induces an AC current. Like a generator. That voltage level is sensed by the ABS computer.

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That answerers that and makes perfect sense. The descriptions on line for ABS systems and HAL sensors are not worded that way, hence my thought direction.



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Re: Brake Problem, ABS kicking in?

Postby Chad91GTZ » Tue Sep 13, 2011 1:14 pm

Yup, it is a hall effect as you stated correctly, which is a pretty generic term for anything that generates a voltage difference as a way of sensing speed as well as many other mesuarable events.


OP, great to hear the the problem is solved! :D


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