Parts Question re: ABS Wheel Speed Sensor

[Zambee500]

I am having a problem with the ABS firing off at very slow speeds as I am coming to a stop. It only happens with light braking. No CELs or warning lights or beeping and the ESP doesn't light up. So everything points to wheel speed sensors from what I am seeing online. I still need to get some trouble-shooting done to see if the current sensors just need to be removed, cleaned and reinstalled, but I was taking an initial look at replacement sensors in case I have to go that route.

For the wheel speed sensors, do our cars require a genuine VW OE part like with the CV axles and various other parts? Or will after-market work just fine? I am seeing around $120 for fronts and $195 for rears from the dealerships, but the aftermarket prices are a fraction. Flennor, Delphi, Beck/Arnley are in the $40-$80 price range. Bosch about $80-$90. And I am seeing PEX for $30-$40 which claim to be mfr'ed in Hungary or Germany and is an OEM for certain VAG, BMW, Porsche, M-B and GM parts.

I don't want to put chineseum crap on if it won't work, but that's quite a price spread. So thought I would check in here. What say the experts? Thanks.

 

[otty]

Are you sure it is your ABS activating? I believe the ABS and ESP lights activate on the dash when ABS is activated.

For a while I thought the same thing was happening with my car (because I kind of felt like ABS activating at slow speeds coming to a stop) but it turned out to be a failing control arm that would flex and move during braking.

 

[Zambee500]

Are you sure it is your ABS activating? I believe the ABS and ESP lights activate on the dash when ABS is activated.

For a while I thought the same thing was happening with my car (because I kind of felt like ABS activating at slow speeds coming to a stop) but it turned out to be a failing control arm that would flex and move during braking.

Hmmm. I need to get VCDS reading of the sensors, which I will have done soon. So maybe I am putting the cart ahead of the horse.

When it happens, there is a pulsing in the brake pedal and a strange sound sort of like a hissing sound, as (what I assume to be) the ABS fires off. The pedal flutters it drops a little bit, like it's just a little mushy and then it firms up again and stops without a problem. Only happens as I'm almost to a complete stop with light braking, like in rush-hour stop & go traffic. If I punch the brake pedal right before I stop for a stronger stop it doesn't do it at all.

 

[imo000]

Can you get on the brakes hard enough to activated the ABS?

 

[algirdas]

I had low speed abs triggering on my Audi.
Turned out to be the tone ring on a rear axle was cracked.
Worth checking.

 

[Tdijarhead]

If your abs light is not on continuously then your sensors are probably ok. I would check the items mentioned above. Dirty, broken , cracked tone ring or flexing in the suspension of some kind is a more likely culprit. The VCDS will tell you what wheel to look at. It will probably tell you that one of your wheel sensors has an intermittent signal. That will be the wheel to look at more closely.

 

[Seatman]

When mine did this it was the sensor on it's way out, it eventually came up with a light on the dash. You know it's the abs as you can feel it through the pedal as well as hear the pump.

Some garages have machines that can read live data but if you're like me just wait till it fails properly then scan it.

Might be worth checking the sensor is in properly, there's not really anything holding them at the right distance from the reluctor ring. Just a sprung loaded bit of metal around it to hold it in the hole but it can move in or out, no fixed point like other cars.

 

[Zambee500]

Thanks everyone. Will check these items (rings, suspension, sensors seated properly, etc.) and report back. Probably have to wait until the weekend though, so this thread may go dormant for the next few days.

You know it's the abs as you can feel it through the pedal as well as hear the pump.

That seems to be what is happening. To the question by imo000, I will try an emergency stop to see if i can activate the ABS in that manner.

Thanks again for all the pointers.

 

[bbob203]

I had a problem with and kicking on turned out the sensor was popped out of the hole a bit pushed it back in and been fine ever since.

 

[Zambee500]

To button this one up from 6 weeks ago, and resolution for any future thread searches, it appears the front right wheel sensor was dirty or not fully/properly seated. Road test with VCDS indicated it was the front pax-side wheel that was reading just a hair slower than the other 3 wheels, so we knew to start there. Took out the wheel sensor, cleaned it and reinserted and it's been fine so far.


Just to recap, no ABS or brake light or ESP light when the ABS was firing off under very light braking as approaching a stop. And the ABS was still working fine at normal speeds during emergency stopping - I was able to engage ABS at will when getting on the brakes hard.


Thanks to the group here for the pointers. Half hour labor (if that) and no parts. I'm sure a stealership would have replaced all the wheel sensors and had me out the door for $650.

 

[otty]

Very interesting. Thanks for the update! I thought I had the problem as a loose control arm but it still occurs.

It is just as you said - during slow braking an ABS firing feeling that can be felt in the pedal with no ABS light activating. I will check my sensors.

 

[Tdijarhead]

VCDS ,worth it's weight in gold to pinpoint the problem area. Glad you got it squared away.

 

[Seatman]

To button this one up from 6 weeks ago, and resolution for any future thread searches, it appears the front right wheel sensor was dirty or not fully/properly seated. Road test with VCDS indicated it was the front pax-side wheel that was reading just a hair slower than the other 3 wheels, so we knew to start there. Took out the wheel sensor, cleaned it and reinserted and it's been fine so far.


Just to recap, no ABS or brake light or ESP light when the ABS was firing off under very light braking as approaching a stop. And the ABS was still working fine at normal speeds during emergency stopping - I was able to engage ABS at will when getting on the brakes hard.


Thanks to the group here for the pointers. Half hour labor (if that) and no parts. I'm sure a stealership would have replaced all the wheel sensors and had me out the door for $650.

What did I win?

 

[Zambee500]

FWIW, the wheel sensor that was off (Front-Right) from the other three sensors at low speeds was only off by a factor of 1. I can't remember the exact numbers (0.1 km/hr or 0.01 km/hr??), but the misreading wheel sensor was consistently off by 1. Not sure how to say it succinctly, but something like:

FL / FR / RL / RR
----------------------
0.5 / 0.4 / 0.5 / 0.5

or

0.05 / 0.04 / 0.05 / 0.05


As those numbers went up or down, they all went up or down together and the Front-Right was under-reporting wheel speed by 1.

 

[Dunno513]

I'm having the same symptoms which started with a new aftermarket hub installed. Shop claims that the abs is not showing up on their scanner when it's pulsing coming to a stop. Just noticed while replacing the brakes that there is quite a gap now between the tone ring and the sensor. About 3/16"

I purchased a new hub and bearing from IDParts knowing full well something was up with the aftermarket hub. I measured the two and I noticed the distance from the hub face to the outer edge of the tone ring was 1/8" less on the aftermarket vs the one from IDParts.

Anyone have similar problems?

This was supposed to be just a simple bearing replacement but shop claims inner race was welded to the hub. I asked to see the part but they claim it had already gone out to the junk pile.

I'll be bringing it back to them on Monday to install my parts unless I can figure out how to adjust the sensor first. What should the gap be?

Thanks for any input.

 

[Dunno513]

So while doing the brakes.... Which the rear pads probably could have gone another 185k.. I noticed that the tab where the abs sensor mounts is bent inwards slightly. It doesn't appear to have moved the abs more than 1/32 or so but clearly it's part of the problem.

Now I question whether or not this was caused by heat from the failing bearing or it was the shop who pulls the entire knuckle off to press out the bearing who pushed on something the wrong way.

Im doubtful the ear can be bent without heating it so I'll grab a used one from the yard to have just in case. This is why I like doing my own work... At least I know how something gets damaged and can only blame myself.

Anyone have any experience with hammering on the knuckle?.... I don't want to add any heat with the bearing right there. Btw...what's the best way to remove the abs sensor? Mine seems to be in there pretty well.

 

[Dunno513]

Picked up a used knuckle just in case but it wasn't needed. After the new hub went on, the problem went away. Shop claims the ear wasn't bent, but I saw what I saw.

Anyone need a right front knuckle with a good hub and ball joint?