# ABS Warning light on after wheel bearing replacement.



## Stinky999 (Sep 14, 2006)

I had the drivers side rear wheel bearing replaced and now the ABS warning light is on. The shop also replaced the wheel speed sensor. The car appears to drive fine and the brakes work fine, although without ABS. The light does not come on immediately upon start up. It normally will appear after the car is driven a bit, could be a few hundred yards or a mile. 

My first thought is that whatever it is that serves as a "trigger" for the speed sensor got damaged during bearing replacement. I don't know what this trigger is, or exactly where it is located, presumably in the hub. I'd welcome any thoughts or suggestions.


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## Dangerrous (Sep 14, 2014)

If it's a general VAG abs sensor type, there's a metal perforated ring around the cv joint hub, usually around 42 perforations , the sensor is charged through inductance by a small magnet working in close proximity to the metal ring, if the sensor is too far away it won't be charged enough to send an ac signal to the abs ecu, a vcds readout will let you know the exact problem.
D


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## Stinky999 (Sep 14, 2006)

Dangerrous said:


> If it's a general VAG abs sensor type, there's a metal perforated ring around the cv joint hub, usually around 42 perforations , the sensor is charged through inductance by a small magnet working in close proximity to the metal ring, if the sensor is too far away it won't be charged enough to send an ac signal to the abs ecu, a vcds readout will let you know the exact problem.
> D


Do you know if there is anyway to adjust the sensor? It appears to just bolt on to the knuckle.

Roger


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## phaetonjohn (Oct 24, 2014)

Roger,

I just had my front right wheel bearing replaced about a week ago, but I have had no lights on. It is possible that a wire got cut. My bearing was corroded on quite badly. It took them 2 hours to get it off!

-John


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## Stinky999 (Sep 14, 2006)

They said the axle was frozen to the hub, so they had to remove the knuckle to get it off. I suppose they may have snapped a wire further up in the harness. Again, they replaced the speed sensor itself. I'll see if I can trace the wires further.

Roger


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## PowerDubs (Jul 22, 2001)

On my wife's '03 GTi, we had an ABS fault last year.

I replaced the offending wheel sensor, but the fault remained.

I bought a new harness that plugs into the sensor and once I replaced that, the fault cleared.

Easy enough to do on her car since it is a hatchback and was a rear wheel. The harness splices inside the car which just required folding the seat down, pulling a piece of trim, and lifting the carpet.

On the Phaeton, it may be more involved, but I imagine similar.


I would visually inspect the external part of the harness that you can see. You may be able to spot damage, and correct the issue from there without replacing the harness.


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## Stinky999 (Sep 14, 2006)

PowerDubs said:


> On my wife's '03 GTi, we had an ABS fault last year.
> 
> I replaced the offending wheel sensor, but the fault remained.
> 
> ...


This is encouraging. Thank you.

Roger


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## cbh123 (Aug 25, 2013)

Is there a reason the shop not owning up to their issue? 
It seems from your very short explanation that they f'ed it up. 
Geeze abs wheel speed sensors have been for the most part unchanged for over 30 years now...

Changing a wheel bearing can involve a bunch of whacking with a hammer if they don't use appropriate pullers. 
One missed swing will damage/destroy any wires/sensors in the way. 

A good hacker might even light up a torch... Equally effective at killing electrical stuff.

Have you looked at the area they worked on? Ask them to put it in the air, look at all wires etc in the area.


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## Stinky999 (Sep 14, 2006)

cbh123 said:


> Is there a reason the shop not owning up to their issue?
> It seems from your very short explanation that they f'ed it up.


Yep, valid point. Without getting into all the details, let's just say that I don't have the time to help this small independent shop to learn about Phaetons. I don't think they are bad guys, this is just outside of what they normally do. In hind sight, I should not have taken the car there, but that is done. I've just decided to move on.

Roger


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## invisiblewave (Sep 22, 2008)

Stinky999 said:


> Yep, valid point. Without getting into all the details, let's just say that I don't have the time to help this small independent shop to learn about Phaetons. I don't think they are bad guys, this is just outside of what they normally do. In hind sight, I should not have taken the car there, but that is done. I've just decided to move on.
> 
> Roger


Probably a smart move. I made the mistake with my local VW dealer of constantly taking it back to them to fix the problems they caused last time I took it back to fix the problems they caused last time I took it back to fix the problems they caused........ it was there for 6 months all told.


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## phaetonjohn (Oct 24, 2014)

The VW dealer nearest me is totally stupid. I take it to a privately-owned garage, and they are great.

-John


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## Stinky999 (Sep 14, 2006)

I just thought I'd put a little update out here. I haven't fixed it yet, but I've been driving it and making some observations. I find it a bit strange that the ABS warning does not come on instantly when you start moving. In some cases, I can drive for several miles, 15 min, before it comes on. But then other times, it comes on within a 100 yards or so. It would seem to me if the wiring harness was damaged, and the circuit was broken, it would come on consistently when the vehicle started moving. It would seem very unlikely to me that the system could last for several miles and/or 15 min without a signal from a sensor, and not throw the error message. But I'm certainly not an expert on this system.

Another thing I noticed is that sometimes, when you first start moving in the vehicle, before the ABS warning comes on, you can feel a tug or two at the brakes. I assume this is the system trying to figure out what's going on. But again, I find it interesting that the error message does not come immediately following this behavior. The first couple times I felt this, I thought the ABS light would come on for sure. Nope. Keep on driving some more, then it comes on. Once the ABS error comes on, the brakes work fine...just without ABS.

I haven't gotten around to getting the VCDS software. Hopefully within the next couple weeks. I'm hoping that may shed a bit more light on what is actually causing the problem.

Roger


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## PowerDubs (Jul 22, 2001)

Did you check to see if it is just as simple as the sensor wire not clipped back in place properly and the tire wore 3/4 through it?


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## Stinky999 (Sep 14, 2006)

PowerDubs said:


> Did you check to see if it is just as simple as the sensor wire not clipped back in place properly and the tire wore 3/4 through it?


Yes I did. I didn't trace the wiring up the axle to see if it shows any signs of damage further up. I plan to do that shortly.

Roger


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## cbh123 (Aug 25, 2013)

Acting like one of a couple things
- I am not sure of the phaeton's exact system for getting wheel speed pulsed signal, but there are two typical methods on most cars. Sometimes there are a bunch of magnets embedded in the bearing dust seal that rotate in front of a sensor, and other times there is a toothed aluminum or Steel ring on the axle shaft (cv joint ) that rotate in front of the sensor. 

The sensor is attached to the hub (right near the bearing usually) and if a grinder was used during the work, iron filings can stick to the magnets or to the sensor depending on the type of system. This can screw up the speed signal only when moving. 

The toothed ring can be physically damaged, missing teeth, corroded, etc, this also can screw up the signal when moving. 

The wiring of course moves with suspension movements, and if there is a crack in the copper wire this can also screw up the signal only when moving. 

I chased very similar symptoms on my jag and it drove me crazy. I changed sensors, inspected the wiring and changed the ring that makes the pulse, but the intermittent fault persisted. 

In desperation, I hooked up a continuity tester (multi-meter that beeps when probes touch) to each wire between the sensor connector and the abs module, one by one - and wiggled the wiring. It was a PITA but finally I found the defective wire, and repaired it - the problem never came back. In my case there was damage to the wire internally - the wire looked Undamaged from the outside. 

someone is going to have to get up close, and dirty (nose touching dirty with flashlight and magnifying glass lol) and inspect the sensor, ring, and wiring. VCDS will be useful to tell you which wheel is giving the fault - there is a possibility that it is not related to the bearing change, and coming from another corner of the car. 

All symptoms point to an intermittent or inconsistent speed signal, but I highly doubt that continuing to observe symptoms will lead you any closer to the solution. 

Keep us posted


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## Stinky999 (Sep 14, 2006)

cbh123 said:


> Acting like one of a couple things
> - I am not sure of the phaeton's exact system for getting wheel speed pulsed signal, but there are two typical methods on most cars. Sometimes there are a bunch of magnets embedded in the bearing dust seal that rotate in front of a sensor, and other times there is a toothed aluminum or Steel ring on the axle shaft (cv joint ) that rotate in front of the sensor.
> 
> The sensor is attached to the hub (right near the bearing usually) and if a grinder was used during the work, iron filings can stick to the magnets or to the sensor depending on the type of system. This can screw up the speed signal only when moving.
> ...


I definitely appreciate the suggestions. I've had my son's 944 Turbo torn apart in my garage for the last 3-4 weeks, so I really haven't had a chance to chase this down. Santa brought me a 9000 lb lift for Christmas which should make it a little easier to trace down the problem (once I get the 944 off of it!).

I'll update as soon as I learn anything new.

Roger


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## invisiblewave (Sep 22, 2008)

If the 951 is really "torn apart", it'll be more than a few weeks before your lift's available!


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## Stinky999 (Sep 14, 2006)

invisiblewave said:


> If the 951 is really "torn apart", it'll be more than a few weeks before your lift's available!


Tell me about it. This car is even less fun to work on than the Phaeton. I should probably clarify that it WAS torn apart; rod bearings, rebuilt turbo, new radiator, etc. Got it 98% done on Sunday and fired it back up, ran great. Still need to tidy a couple minor things up tonight, but it will be on the road on Friday. I'm driving it up to Elkhart Lake, WI (not quite Road America season yet).

Roger


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## invisiblewave (Sep 22, 2008)

Mine's leaking from that oil pan seal, which means it's also going to be time for rod bearings. I think it's beyond my abilities though.


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## Stinky999 (Sep 14, 2006)

invisiblewave said:


> Mine's leaking from that oil pan seal, which means it's also going to be time for rod bearings. I think it's beyond my abilities though.


I consider my mechanical abilities above average, having performed an engine/tranny swap on my 911, tearing trannys apart, timing belt replacement on the Phaeton, etc., etc. But doing this work on the 951 was the biggest PITA (and that's using a lift as well). To get to any one thing on this car, you have to remove 3-4 other things. I don't know what a shop would charge to do this, but I wouldn't be surprised if it was $2000.

Roger


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## invisiblewave (Sep 22, 2008)

Yeah, I think it's a 12 hour job or something, which is why I've just been cleaning up the oil spots on the garage floor! They're always leaking a few spots from somewhere anyway.


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## Stinky999 (Sep 14, 2006)

*ABS issue update...*

I purchased the VCDS software and ran a scan. It showed the left rear sensor as the problem, which makes sense, since that was the wheel that had the bearing replaced. I pulled the sensor and checked the part number on it and it turns out when the shop replaced the sensor, they used the part number for the left front/right rear, instead of the right front/left rear. I bought the correct sensor, installed it, and the light went out and the error code cleared. That's the good news.

The bad news is that the ABS system is still not working properly. When coming to a stop, the brakes will pulse a couple times as the speed falls below 20 mph. No lights come on, no error codes are generated. And the pulsing only seems to occur around the 20-15 mph range. If you hit the brakes at 60 and slow to 40, they seem fine. Conversely, if I leave it in gear and idle around a parking lot, stopping and starting, the brakes feel fine.

Any suggestions?

Thanks.
Roger


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## cbh123 (Aug 25, 2013)

There is a way to capture live readings from each sensor with vcds 
Either record them in a graph or data table.
Is is not the most intuitive thing, I did it last week for someone with a turbo Jetta. We were gathering boost / timing info for his ecu tuner. 
I'd have to have my laptop up and running to figure it out again. 

But sounds like one wheel speed is dropping below the threshold or to zero, that indicates it is locking up. 
It sure is tempting to jump to conclusions, but since you have the tool, (vcds) use it, 

A bad wire or loose connection anywhere that moves with suspension movement?


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## Stinky999 (Sep 14, 2006)

cbh123 said:


> There is a way to capture live readings from each sensor with vcds
> Either record them in a graph or data table.
> Is is not the most intuitive thing, I did it last week for someone with a turbo Jetta. We were gathering boost / timing info for his ecu tuner.
> I'd have to have my laptop up and running to figure it out again.
> ...


I'll send a message to Ross Tech and see if they can guide me towards this procedure. 

With respect to the loose connection theory, I think if the sensor lost connection, it would send an error code to the ECU and activate the ABS warning light. This is what it was doing with the incorrect sensor installed. 

I'm thinking that the toothed wheel that is read by the sensor may be damaged or improperly installed. Unfortunately, I think I need to go through much of the process to replace a wheel bearing to get at this. My desire to avoid this process in the first place is what probably got me in the position that I am in now.

Roger


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## Stinky999 (Sep 14, 2006)

Does anyone know where the toothed/tone ring is on a Phaeton that is read by the wheel speed sensor? I don't see any separate part shown in the parts diagrams for this, and none of the photos I could find showing hub/wheel bearings have any sort of visible ring. Most other VW models have a separate ring that is attached to the hub. Apparently the Phaeton uses something else. I realize I will have to pull the rotor and possibly the axle/hub to figure out what is going on, I just would like to see a diagram or picture first before I start taking it apart. 

Thanks.
Roger


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## cbh123 (Aug 25, 2013)

Beyond suspicion, how do you know what wheel to take apart?


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## Stinky999 (Sep 14, 2006)

I had the left rear wheel bearing replaced and this problem started (it's all outlined in prior posts).

Roger


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## PowerDubs (Jul 22, 2001)

Stinky999 said:


> Does anyone know where the toothed/tone ring is on a Phaeton that is read by the wheel speed sensor?




Roger,

If I am not mistaken, the sensor on the Phaeton is mounted to the suspension upright (because of the bolt on wheel bearing design) so the toothed wheel is between the axle and the upright, cupped inside.


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## cbh123 (Aug 25, 2013)

Stinky999 said:


> I had the left rear wheel bearing replaced and this problem started (it's all outlined in prior posts).
> 
> Roger


Yes, this is what I meant by suspicion. 
It is very tempting to assume the issue lies there, but since you have the vcds, you should be able to prove the signal (well, lack of signal - indicating a skid) that triggers the abs originates there. 
Just trying to use diagnostic power to its full advantage. 

The "tone ring" will be within a millimetre or two of the tip of the sensor you already replaced. If you pull out the sensor, and look through its mounting hole, you should see it. Turn the wheel slowly with the sensor out, (hard with AWD CAR- and other wheels on ground) - watch for damage.

Keep in mind the phaeton DOES NOT USE a typical toothed ring. It uses embedded magnets in a flat surface. These magnets pass in front of the sensor, generating the signal.

It is explained a little on pg 48 of the chassis self study program.


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## Stinky999 (Sep 14, 2006)

"Keep in mind the phaeton DOES NOT USE a typical toothed ring. It uses embedded magnets in a flat surface. These magnets pass in front of the sensor, generating the signal."

This is what I needed! Yes, I already tried looking in the sensor mounting hole with the sensor removed. Unfortunately, my fat head doesn't really fit very well between the dust shield and the fender well. But from what I could see, I did not see any sort of a toothed wheel in there. Also, tried rotating the wheel a bit (obviously won't move much) with a small screw driver inserted to see if it "clicked" against teeth. Nothing. So your description of a smooth surface with embedded magnets helps to explain this.

With respect to the the VCDS scan, when the ABS light was on, it identified a "mechanical fault" with the left rear sensor. This is how I discovered that the shop had installed the incorrect sensor for that wheel (explained above). With the correct sensor installed, the ABS light does not come on, and no fault codes are generated for the ABS system, even though it behaves erroneously. 

cbh123, I know you mentioned being able to capture individual wheel sensor data while the car is driving. I still haven't figured out how to do this. I tried driving around the block with the VCDS hooked up, but system erred out (something like "too much data...". 

Thanks for the suggestions. I'll keep working on it.

Roger


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## Stinky999 (Sep 14, 2006)

I'm getting back around to fixing this. I still think the issue has to lie with the replacement wheel bearing, either it's design or installation. The bearing that I purchased was a SKF sold by Rock Auto (SKF FW81). There is nothing visible on the bearing itself that would appear to resemble any sort of actuator ring. I know in an earlier reply, I was told that this ABS system uses embedded magnets versus the traditional ring. However, I was looking at another thread here on the forum that describes wheel bearing replacement. In the images on p. 7 of the thread, you can see the wheel bearing/hub assembly after it was removed from the carrier arm. It appears though there is a ribbed ring that would be very much in line with where the ABS sensor tip should end up. http://forums.vwvortex.com/showthread.php?3109773-Wheel-Bearing-Discussion/page7 I am wondering if anyone can elaborate on this? I am preparing to take my suspension apart to get at the bearing to see if indeed there is a similar ribbed ring, or anything else that looks like it should be serving as an actuator of any kind.

Thanks.
Roger


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