ABS Sensor Error @ 50 km/h

[blaahvalen]

Hey forum!

Long story short: I had a bad wheel bearing on my '12 Ibiza 1.2 TDI, and when replaced the mechanic noted that the ABS-sensor was damaged during the repair. Pretty common so no big deal. Since he didn't have the part or the time that day, I decided to buy one myself and replace it since I had a long trip coming up and could really use the cruise control (which doesn't work with a faulty sensor)

I replaced the sensor, and all errors (ABS, ESP, Tire Pressure) was cleared upon the next drive - but only up until 50 km/h where they re-appears. If I shut off the car and restart it, they're gone again, but reappears at almost exactly 50 km/h once more. I can keep repeating this pattern, so something seems to trigger the errors at around that speed.

Have I gotten a faulty sensor or could there be another issue here? All ideas welcome!

Regards

 

[blaahvalen]

No takers?

I had to buy the sensor from the only place that's open on a Saturday afternoon and they usually sell poor quality parts, so could it be as simple as a bad sensor?

 

[cairus]

the correct wheel bearing installed?

 

[blaahvalen]

the correct wheel bearing installed?

I'm fairly certain, pretty sure I double checked before ordering. It's a LUK / FAG 713610470 which should match the OEM 6Q0407621BR and similar

 

[cairus]

Did you get the spare part number from your Seat dealer using the VIN?

 

[RUM4MO]

Surely if it is the correct diameter and fits, it is okay, also hopefully as it works up to 50KPM it must have the magnetic element fitted to it, FAG 713 6104 70 is exactly what I fitted to both sides of my wife's 2015 VW Polo 1.2TSI 110PS 6MT 18 months ago, and they are still okay as is the ABS etc.

I've really not got much help to offer, these ABS front sensors do normally get destroyed/broken if left in when the bearings are being replaced, though the possibility of removing them first to avoid that happening, especially if the car is used in a region where salt is used in winter, is also normally going to destroy them. I must admit that I got lucky, and one side, maybe the LHS ABS sensor is still okay after being in the hub carrier while replacing the bearing - the RHS one got caught on the rust and was pulled side ways and so cracked its casing - so I replaced it before putting the car back together.

How did you clean up the hole in the hub carrier - I used suitable sized drill bits - but then I probably cleaned that hole up before fitting the new bearing into it, I bought a Bosch branded sensor although the original one was TRW branded as it would have been TRW that would have been supplying VW Group with complete front assemblies to the car assembly plants. The TRW original one had aluminium alloy metal insert part round about the fixing screw/bolt, the new Bosch sensor had what looked like brass metal insert part round/at the fixing screw/bolt.

This could end up just being due to a "bad" copy part causing a lower than expected "pick up" from the magnetic element on the rear face of the bearing.

Good luck!

 

[blaahvalen]

Hey, apologies for the late response! Appreciate the input. Busy week.

So we decided to take the easy approach first and replace the ABS sensor with a new one from a premium brand (ATE), but we're experiencing the exact same issue. So the sensor itself it ruled out with 99% certainty. My mechanic then took the thing apart, and despite me feeling that I was quite careful when struggling to remove the old, stuck sensor, it would seem that I accidentally did a tiny bit of damage to one of the "magnetic teeth" or whatever you'd call it inside the new wheel hub/bearing.

So chances are that it might be my own fault, and I'll take my chance and let the mechanic do another replacement of the wheel bearing - hopefully with a succesful result. Guess mistakes makes you poor in money and rich in experience.

I'll post an update when/if it's fixed.

 

[RUM4MO]

So chances are that it might be my own fault, and I'll take my chance and let the mechanic do another replacement of the wheel bearing - hopefully with a successful result. Guess mistakes makes you poor in money and rich in experience.

I'll post an update when/if it's fixed.

Yes, I agree!

When I replaced both front bearings on my wife's 2015 VW Polo 1.2TSI 110PS 6MT, I had never ever worked on these GEN2 hub/bearing kits, bought a cheap China (probably) made kit and a set of better quality forcing pins as I'd read that the cheap China made forcing pins in these kits was the weak part, that job, though a bit worrying as it was the first time, went well apart from bending/breaking the RHS ABS sensor.

One thing though, I'm certain that any time that I've looked at VW Group workshop manuals, they always show a picture of these bearing - but the type used on the rear of these cars, ie roughly the same design as the front ones, but for the rear the GEN2 bearing comes pressed into a small hub mounting plate that just bolts onto the rear beam axle - but, the pictures show that assembly placed rear end (magnetic face) down and a large red cross - then shows that assembly placed rear end (magnetic face) upwards and a large green "tick" implying that the magnetic end is very fragile. I only found that out after replacing the front bearings, so maybe I was lucky or handled that assembly in a way that did not cause it any damage - so maybe not completely your fault.

Edit:- though as I said, I did clean out the "hole" that the ABS sensor "lives" in while the bearing was out of the hub - so I wonder what is the correct way to clean out that hole if an ABS sensor needs replacing but the bearing is not being replaced!

 

[RUM4MO]

I've just had another thought, if this new bearing/hub has not been fully pulled into the hub carrier, and its locking element/cage fully engaged, then it might not be in far enough and not locked in place. This could/would lead to the gap between the ABS sensor and the magnetic surface being too big - which would lead to the ABS sensor not picking up a signal well enough. Also if this new bearing is not locked in place, it will "walk" out of the hub carrier slowly with time.

Unfortunately, if that bearing gets removed it will now be unserviceable as its retaining cage will have been destroyed on removal.

Finally, I'm guessing that a scan tool has been used to prove that it is this wheel's ABS sensor that is the source of the incorrect signal - and also checked that the wiring is correct and that any errors relating to this wheel's ABS sensor are really from this sensor and not another wheel's ABS sensor.

 

[blaahvalen]

I've just had another thought, if this new bearing/hub has not been fully pulled into the hub carrier, and its locking element/cage fully engaged, then it might not be in far enough and not locked in place. This could/would lead to the gap between the ABS sensor and the magnetic surface being too big - which would lead to the ABS sensor not picking up a signal well enough. Also if this new bearing is not locked in place, it will "walk" out of the hub carrier slowly with time.

Unfortunately, if that bearing gets removed it will now be unserviceable as its retaining cage will have been destroyed on removal.

Finally, I'm guessing that a scan tool has been used to prove that it is this wheel's ABS sensor that is the source of the incorrect signal - and also checked that the wiring is correct and that any errors relating to this wheel's ABS sensor are really from this sensor and not another wheel's ABS sensor.

Those are interesting thoughts. New bearing is on the way, but I'll throw these words at my mechanic before he starts any work. He does seem to know his stuff and I've used him basically always, so I'd be surprised if his work is the issue.

 

[BadBoy03]

Those are interesting thoughts. New bearing is on the way, but I'll throw these words at my mechanic before he starts any work. He does seem to know his stuff and I've used him basically always, so I'd be surprised if his work is the issue.

Hi.
I'm from the MK1 LC section, but interested in your thread.
I am having a wheel bearing replaced on Friday & abs light is on, so I am hoping this will all be corrected like you.
It's an interesting problem you've got, although pain in the arse may be more fitting. If you have no luck once replacements finished, a scan should confirm the issue & where.
Best of luck

 

[blaahvalen]

So an update:

It was most likely my own fault. As said my mechanic found a teeny tiny bit of damage to the bearing, which was probably caused by myself trying to pry out the old, stuck ABS-sensor. Despite it being barely unnoticeable it was enough to cause the issue and new wheel bearing fixed the issue. The car has been running fine for a few days with the same new sensor since the first replacement, so we assume the problem is fixed now.

Appreciate all the input - and be careful when removing those stubborn bastards. Given how relatively cheap ABS-sensors are, in case another wheel bearing needs replacing in the future, I'll probably just ask my mechanic to pry out the ABS-sensor and replace that at the same time. Northern climate, salty roads and small plastic sensors is a dreadful combination.

 

[RUM4MO]

Excellent!
If you watch any YouTube videos covering replacing these GEN2 bearings, they all show the ABS sensor being removed before removing the bearing, and all they do is unscrew the small bolt holding the ABS sensor in, and lift the ABS sensor out of the hub! Now, in case there is anyone out there that reads these postings and has never seen these ABS sensors, they are potted in plastic and the sensor's lead section is "waisted" - and this is located into a cast/forged iron/steel lump of metal that has an open hole at the bottom of this "tube" that the ABS sensor is located into - moisture/water/winter salt gets into this "tube" and the hub metal corrodes, this fills up the void where the "waisted" area is and so "locks" the ABS sensor in place - so on all the YouTube videos that I've seen, I think that this task has been rehearsed before being videoed - which saves a lot of time but gives the poor home car fixer a false idea of the task ahead! Maybe I've written about this earlier on this thread, but I seem to remember that VW Group "talk" about basically "getting the ABS sensor out" as opposed to "removing it for future reuse" - if you have ever carried out this GEN2 bearing task, you can probably understand why their workshop manual is written that way!

So, if I ever need to replace another one of these GEN2 bearings, I'll buy a new ABS sensor every time to avoid this disappointment, my previous experience alerted me to this possibility and your experience has confirmed that doing that is the proper way to do this job, just a pity that your mechanic had not thought the same.