Rear wheel speed sensor issues

[ianlovatt]

I've got this fault code:
Address 03: ABS Brakes Labels: 8E0-614-517.lbl
Part No: 8E0 614 517
Component: ABS/ESP front 4329
Coding: 04255
Shop #: WSC 06435
VCID: 65C61642FFC98B16CE-5120

1 Fault Found:
00287 - ABS Wheel Speed Sensor; Rear Right (G44)
30-00 - Open or Short to Plus

I've tried clearing it in VCDS to see if it's just temporary but it immediately reappears so presume the issue is always present. If I use the measure blocks and read the wheel speed sensors it does increase to the same as the others but appears lag behind which makes me think the signal is noisy/distorted in some way or suffers bursts of interference. I've had a hunt around on here for info on these sensors but not found anything. This is the first time I've had to post after following other threads on my quest to solve my ESP and ABS warning lights:
ESP & ABS warning lights on
I've had the wheel off and poked around at the sensor but the retaining bolt (torx t30?) was being stubborn so before I sheared it off I thought I'd put my hand up and review my options. I've also got to the connector under the back seat and was expecting to find some sign of a dodgy connection but alas it's all dry as a bone and the pins look in good shape. I noticed the sensor is magnetic so I'm guessing it's a reed switch of some sort. I stuck the multimeter across the pins from the sensor when i unplugged it and it read open circuit presumably if I could rotate the wheel at some point it would close. I guess that doesn't really tell me much as it appears 'some' signal is getting through given the readings do increase in VCDS.

As the MOT is due by the end of the month I'm running out of time to sift through the internet so if people can advise on the following that would be much appreciated:
What are the usual failures on these sensors?
Are the symptoms I'm describing possible to fix without having to renew the part?
If I should just renew it how much should I expect to pay and is it worth going for genuine audi parts?
Am I being a total numpty with how I'm using VCDS (first go with it)?

The car is a 53plate 1.9tdi avant and in case it helps for context a full scan can be found here:
Dropbox - Log.txt

Cheers,
Ian

[Doctle Odd]

A wheel speed sensor is just an ABS sensor, quite cheap and easy to replace. Check the ring before you remove it, make sure its not loose or bent. The sensors tend to break on the way out, check the wiring back to the connector too. After you replace the sensor clear the fault code, should be job done.

[ianlovatt]

Thanks for replying, so it's probably best to just swap it out then?

I think I've found a good series of steps to follow:
Audi A4 B6 ABS Wheel Speed Sensor Replacement (2002-2008) | Pelican Parts DIY Maintenance Article
Looks like it's just a 5mm allen bolt where I was trying my torx t30.

Slightly confused about the ring you refer to and they also mention it in the link above. Hopefully that'll become clear once I have it in bits.

Also there seems to be some good info on front sensors here:
Wheel speed sensor replacement

[Doctle Odd]

The ring runs a couple of mm from the sensor looks something line this

abs.jpeg

[zollaf]

they work like this, the sensor is a magnet surrounded by wire. the ring spins very close to it and causes an induced voltage in the sensor. the faster you go, the bigger the voltage. if all 4 voltages as read by the ecu are the same, then all is ok. if when you brake one or more voltages decrease more than the others then you are skidding and the ecu can engage the abs pump to release pressure at that wheel, many times a second, so you are no longer skidding. if you are not breaking and one voltage decreases then the ecu knows all is not well and will shut down the abs, thus putting the warning light on. this may be because of a fault in the sensor or it wiring, or a break in the abs ring, or just that the abs sensor has ridden up out of its mounting hole. some are just pressed into place and a tap into place with a hammer can sort them out. yours are bolted in so this is unlikely, but not impossible.

[Doctle Odd]

they work like this, the sensor is a magnet surrounded by wire. the ring spins very close to it and causes an induced voltage in the sensor. the faster you go, the bigger the voltage. if all 4 voltages as read by the ecu are the same, then all is ok. if when you brake one or more voltages decrease more than the others then you are skidding and the ecu can engage the abs pump to release pressure at that wheel, many times a second, so you are no longer skidding. if you are not breaking and one voltage decreases then the ecu knows all is not well and will shut down the abs, thus putting the warning light on. this may be because of a fault in the sensor or it wiring, or a break in the abs ring, or just that the abs sensor has ridden up out of its mounting hole. some are just pressed into place and a tap into place with a hammer can sort them out. yours are bolted in so this is unlikely, but not impossible.

[Eibbor]

I have had the exact same fault recently. Although It has only appeared when the temperature is low and at the start of a journey which makes me think it may be moisture in the connections. Will give it a check when I have some free time. It hasn't displayed an error in a few weeks but for peace of mind I will probably fire a sensor into it. Helpful thread thanks!

[ianlovatt]

cheers zollaf and doctle odd, I'll check what state the ring is in and give things a wiggle before lashing out on a sensor.

Ours only started doing it this summer on a super hot day in france (~30degC) but was very intermittent at first. Usually just re-starting her would clear it but it's now very rare that it doesn't come on.

[ianlovatt]

Finally got the chance to post a follow up to sorting the speed sensor out (and passing MOT win!):

So here's my sensor after the retaining bolt sheared off and I discovered the sensor still firmly held in place by corrosion:
22102015493.jpg

I then drove an old screwdriver down between the metal plate on the sensor and the mount. Not the best move in hindsight as it damaged the mount slightly and the right hand side (as viewed in the photo) of the sensor sheared off leaving the cylindrical body still inside the mount and projecting in towards the disk through the mudguard/spray shield thing. I ended up getting a hacksaw and chopping up the sensor like sausage and extracting it in bits back towards the mount. This left me with a sheared off bolt in the mount and a cross section of the sensor inside the mount (sheared off on the right and hacksawed flush on the left). Got a punch and drove the final bit of sensor out of the mount and a flexible drill extension to drill out the bolt:
Flexible Drill Shaft 915mm - Toolstation

The bolt's thread and the mount were so rusted together I ended up having to re-tap the m6 thread with more cheapo toolstation kit:
Tap & Die Set 10 Piece - Toolstation

Here's the mount cleaned out:
25102015494.jpg

I got a new bolt from Audi (19p) part number P AN 014 740 11. Audi wanted £105 for the sensor but eurocarparts got me a replacement bosch one for £63. The eurocarparts number is 417 44 0430 and on the packaging it seems to show the bosch part number as 0 265 006 681.

I filed down the inside of the mount so I could slide the new sensor in and put some copper grease around it to hopefully stop it seizing in place. Here it is (you can see the slight gap at the bottom where my screwdriver antics chipped a bit off the mount):
29102015495.jpg

One thing that's worth pointing out to someone like me working on a car raised on axle stands is the gland where the sensor cable enters the body is a sod to push back in place lying scrunched up under the car. I loosened the plastic cover by taking off the bolts on the leading edge of the wheel arch to improve access a bit enough to take the old sensor out but I think you'd need to take the cover off completely to push the new one into place (I got the garage to pop it home when it went for it's MOT a few days later). Also I pulled through a shoe-lace when removing the old sensor so I could use that to pull the new one up through the body into the interior. Here's the offending gland refusing to be pushed into place:
29102015496.jpg


If I'm feeling very diligent I might remove it again and chuck some primer on the mount to stop it rusting so quick.



So last thing that I'm hoping some pro on here can answer is what actually went wrong with my sensor. When I extracted it I noticed that there was some grey gunge on the end of the sensor on the magnetic core that's exposed at the end. I'm wondering if this was some lithium grease that was conductive enough to short the core to the disk and ground the sensor reading? I've never greased up anything on the hub/wheelnuts but we did get the rear disks changed last year so I'm wondering if in the heat of france somehow the grease flowed out from wherever it was and got on the end of the sensor?

Also if this is why the sensor started playing up why is the end of the sensor exposed at all? If there's no good safety reason I might try to cover the end so it can't happen again!

I think I've read on here about 'cleaning' up the sensors but I can't seem to find the post now so I'm wondering if this is what they referred to (making sure the bit of bare core isn't grubby) and that also ties in with what doctle odd said about checking the ring above before removing the sensor. I assumed you'd need to take the whole brake off to get a look at the disk and ring surface so as I needed to keep the car running and haven't played around with rear disk brakes/hand brakes I was a bit intimidated so thought I'd just see what I could do just taking the wheel off. As there's no other obvious signs of damage on the sensor if it was just this shorting of the core to the ring by the grey gunge then perhaps the whole thing could of been fixed by removing the disk and wiping the end of the sensor?!

Any thoughts welcome on this and I hope my struggles save someone else some time in the future

Ian

[mikethebike3]

Finally got the chance to post a follow up to sorting the speed sensor out (and passing MOT win!):

So here's my sensor after the retaining bolt sheared off and I discovered the sensor still firmly held in place by corrosion:
22102015493.jpg

I then drove an old screwdriver down between the metal plate on the sensor and the mount. Not the best move in hindsight as it damaged the mount slightly and the right hand side (as viewed in the photo) of the sensor sheared off leaving the cylindrical body still inside the mount and projecting in towards the disk through the mudguard/spray shield thing. I ended up getting a hacksaw and chopping up the sensor like sausage and extracting it in bits back towards the mount. This left me with a sheared off bolt in the mount and a cross section of the sensor inside the mount (sheared off on the right and hacksawed flush on the left). Got a punch and drove the final bit of sensor out of the mount and a flexible drill extension to drill out the bolt:
Flexible Drill Shaft 915mm - Toolstation

The bolt's thread and the mount were so rusted together I ended up having to re-tap the m6 thread with more cheapo toolstation kit:
Tap & Die Set 10 Piece - Toolstation

Here's the mount cleaned out:
25102015494.jpg

I got a new bolt from Audi (19p) part number P AN 014 740 11. Audi wanted £105 for the sensor but eurocarparts got me a replacement bosch one for £63. The eurocarparts number is 417 44 0430 and on the packaging it seems to show the bosch part number as 0 265 006 681.

I filed down the inside of the mount so I could slide the new sensor in and put some copper grease around it to hopefully stop it seizing in place. Here it is (you can see the slight gap at the bottom where my screwdriver antics chipped a bit off the mount):
29102015495.jpg

One thing that's worth pointing out to someone like me working on a car raised on axle stands is the gland where the sensor cable enters the body is a sod to push back in place lying scrunched up under the car. I loosened the plastic cover by taking off the bolts on the leading edge of the wheel arch to improve access a bit enough to take the old sensor out but I think you'd need to take the cover off completely to push the new one into place (I got the garage to pop it home when it went for it's MOT a few days later). Also I pulled through a shoe-lace when removing the old sensor so I could use that to pull the new one up through the body into the interior. Here's the offending gland refusing to be pushed into place:
29102015496.jpg


If I'm feeling very diligent I might remove it again and chuck some primer on the mount to stop it rusting so quick.



So last thing that I'm hoping some pro on here can answer is what actually went wrong with my sensor. When I extracted it I noticed that there was some grey gunge on the end of the sensor on the magnetic core that's exposed at the end. I'm wondering if this was some lithium grease that was conductive enough to short the core to the disk and ground the sensor reading? I've never greased up anything on the hub/wheelnuts but we did get the rear disks changed last year so I'm wondering if in the heat of france somehow the grease flowed out from wherever it was and got on the end of the sensor?

Also if this is why the sensor started playing up why is the end of the sensor exposed at all? If there's no good safety reason I might try to cover the end so it can't happen again!

I think I've read on here about 'cleaning' up the sensors but I can't seem to find the post now so I'm wondering if this is what they referred to (making sure the bit of bare core isn't grubby) and that also ties in with what doctle odd said about checking the ring above before removing the sensor. I assumed you'd need to take the whole brake off to get a look at the disk and ring surface so as I needed to keep the car running and haven't played around with rear disk brakes/hand brakes I was a bit intimidated so thought I'd just see what I could do just taking the wheel off. As there's no other obvious signs of damage on the sensor if it was just this shorting of the core to the ring by the grey gunge then perhaps the whole thing could of been fixed by removing the disk and wiping the end of the sensor?!

Any thoughts welcome on this and I hope my struggles save someone else some time in the future

Ian

Old post I realise, but just wanted to say a big thanks to you Ian, I had an almost identical situation on my A4/B6 rear right ABS sensor, possibly worse as bizarrely the sensor had been glued in place and had to be taken out piece by excruciating piece - there's an amazing amount of super-fine copper wire in these things! It took some time, but after removal, cleaning up, drilling out the old broken screw (refused to succumb to PlusGas) and tapping the hole again, new sensor (Bosch original, less than £30 from Amazon surprisingly), all's now well. I particularly liked the links to cheap but very effective tools, the flexible extension from Toolstation was just brilliant.
Excellent write-up, much appreciated!
Mike