ABS wheel speed sensor fault - sensor and bearing changed twice

[freeflyer]

Six months ago the ABS warning light appeared on the dash of my Audi A3 1.8 TFSi (2007, 8P).

Using VAGCOM I found that the issue was with the rear right wheel speed.

I changed the sensor but this did not fix the problem, so I changed the wheel bearing (which has the magnetic ring on it) and found that the original was badly corroded. The new wheel bearing fixed the problem and all was good.

Recently the rear pads were badly worn - the pads on the wheel that had the corroded magnetic ring on the bearing were almost down to the metal.

I changed the rear pads but then shortly after the ABS warning light appeared again, Using VAGCOM I found that the issue was with the rear right wheel again !

I could only presume that maybe the worn pads caused the sensor or the magnetic ring to fail, maybe by overheating or debris ?

So, I changed the sensor again but this did not fix the problem, then I changed the wheel bearing again but this did not fix the problem.

I checked the magnetic ring on the wheel bearing I removed using a magnetic viewing film and it seem to look fine...

When I log the wheel speed with VAGCOM and spin the wheel it permanently reads 0kph.

When I unplugged/plugged the sensor I sometimes heard a beep from the dash board and sometimes there was a blip on the signal logged on VAGCOM

I have connected some wires near to the sensor connector to look at the signal on an oscilloscope. The scope shows battery voltage so the sensor is getting power and therefore it cant be a wiring fault, but there are no pulses when I spin the wheel (the level remains at battery voltage).

The sensor air gap can be seen in the picture below...

My MOT is due in a week so I need to get this sorted but I'm at a loss as to what the problem is.

I bought the sensors and wheel bearings from GSF (fortunately with 60% discount)...

https://www.gsfcarparts.com/413vg0450

https://www.gsfcarparts.com/648vg0260

Surely the sensors or wheel bearings cant be faulty having replaced both of them twice ? Or are they very poor quality ?

Has anyone else had this issue or have any suggestions on how to fix ?

The fault description from VAGCOM is below...

Address 03: ABS Brakes Labels: 1K0-907-379-MK60-F.lbl
Part No SW: 1K0 907 379 AC HW: 1K0 907 379 AC
Component: ESP FRONT MK60 0101
Revision: 00H11001
Coding: 0021122
Shop #: WSC 06314 000 00000
VCID: 73EE262112AD8DDC2A-8026

1 Fault Found:
00287 - ABS Wheel Speed Sensor; Rear Right (G44)
008 - Implausible Signal - Intermittent

 

[aqibi2000]

have you confirmed the one side is getting vbatt, but the other will be to ground to be present? Continuity tea to Gnd. Just compare this with another sensor on the vehicle. This seems to be a plausible factor if your readings were valid

 

[freeflyer]

No the scope is on DC coupling, it’s showing a voltage level of 12V DC but no pulses when spinning the wheel.

The sensors are 2-wire current sensors (not 3-wire voltage sensors). There is usually a pull down resistor in the control unit to convert the current to a voltage which then goes to a comparator to detect the different levels.

I can only think it’s an air gap or alignment issue?

I haven’t tested any other sensors yet

 

[aqibi2000]

Being 2 wire sensors if you swap the connector (further up stream usually in the boot) between the left and right rear wheel speed sensor and see if the fault changes position you can rule it to be either the :

wiring from that point to the abs module (ground related) or the abs module itself sending more current than what the sensor can sink.

The above only applies if scope getting its ground reference not from the actual sensor. Otherwise as you say it can be air gap related

I initially was assuming it's the 3 wire hall effect

 

[Nessy]

I can’t really add much as I haven’t had this problem, but I’d make sure the bearings and sensor are the very best quality , I dislike seeing things like “standard” quality on a website.
Having done my own rear bearings a few weeks ago (due to wear and tear of the old bearings) it’s not a job I’d like to do again, the procedure is easy (and quick!) enough , but torquing that splined bolt up to 180Nm and then another 180 degrees was rather nerve-wracking.
Out of interest, what brands of bearing have you been using?
I’d stick to an OEM brand like FAG or SNR , I used FAG.

 

[freeflyer]

If you swap the connector (further up stream) between the left and right rear wheel speed sensor and see if th4 fault changes position you can rule it to be either the wiring from that point to the abs module or the abs module itself

I did think of trying this but I don’t know where the connector further up stream is?

I can see the wiring go from the sensor into the wheel arch liner (behind a plastic fuel pipe as it’s on the same side as the fuel filler) but I don’t know the route it takes to get to the abs module?

 

[freeflyer]

I can’t really add much as I haven’t had this problem, but I’d make sure the bearings and sensor are the very best quality , I dislike seeing things like “standard” quality on a website.
Having done my own rear bearings a few weeks ago (due to wear and tear of the old bearings) it’s not a job I’d like to do again, the procedure is easy (and quick!) enough , but torquing that splined bolt up to 180Nm and then another 180 degrees was rather nerve-wracking.
Out of interest, what brands of bearing have you been using?
I’d stick to an OEM brand like FAG or SNR , I used FAG.

I had a 1 meter breaker bar to do the extra 180 degrees but because the bolts were those horrible torx type I struggled to get 90 degrees.

I’ve replaced the stretch bolts on the front wheels (when replacing the cv boots) which used the 12 spline type bolts and I managed to do 180 degrees on those.

The wheel bearing was the standard type from gsf (see link in original post).

The second bearing I bought was slightly different to the first bearing I bought, despite it being the same part number from gsf.

 

[aqibi2000]

I did think of trying this but I don’t know where the connector further up stream is?

I can see the wiring go from the sensor into the wheel arch liner (behind a plastic fuel pipe as it’s on the same side as the fuel filler) but I don’t know the route it takes to get to the abs module?

Usually under passenger seats

 

[aqibi2000]

Found this for you he follows the same process I suggested

 

[freeflyer]

Found this for you he follows the same process I suggested

Thanks I saw that the other day so I lifted up the rear seats but didn’t find anything. The car in his video is not a 5 door A3.

 

[ScottyP45]

No the scope is on DC coupling, it’s showing a voltage level of 12V DC but no pulses when spinning the wheel.

The sensors are 2-wire current sensors (not 3-wire voltage sensors). There is usually a pull down resistor in the control unit to convert the current to a voltage which then goes to a comparator to detect the different levels.

I can only think it’s an air gap or alignment issue?

I haven’t tested any other sensors yet

Hi mate, if you have a 2 wire sensor which switches current, you can't connect the scope across the sensor wires as that's meaningless, you won't see anything. All you're doing there is reading the 12v sensor supply returning to gnd through the pull down. You need the scope gnd on the battery neg and the input probe on both sensor wires one at a time. One lead will give 12v and the other the switching voltage at 2v range.

See here:

https://www.tiepie-automotive.com/en/articles/abs-sensor-hall

 

[freeflyer]

Thanks ScottyP45 you’re right I was being dumb and measuring it wrong! I’ll try again and measure correctly

I thought I had ruled out the abs control unit but that’s because I measured the signal wrong. So if I see a signal on the scope this time then that confirms it’s the abs control unit

I’ve never changed an abs control unit before, I’m wondering how difficult it is. I struggled to bleed the brakes on a Peugeot I had years ago so I’m not keen on messing with brake bleeding again

 

[ScottyP45]

If you have to end up changing it, I'm sure you can swap the ABS ECU without touching the hydraulic block. Part numbers need to match exactly though if you leave the pump in place.

 

[Al001]

Thanks, if you're still around, your post helped me (magnetic film diagnosed the brand new SKF wheel bearing was defective from factory, which made a hard diagnosis even worse). Hope you managed to get to the bottom and sorted it.

Posting this to help the next poor sod along who finds this thread in web search results because I've spent weeks and hundreds of pounds fixing a similar problem.

I was using VCDS to graph the output of all the ABS wheel speed sensors (car on axle stands, wheels off, rotating the axles using my foot on the brake discs) to try to get similar wheel speeds from each corner. I was seeing very low speeds on the rear right, high on rear left and the front left and right looked normal. This is not a dead ABS module (no communication error message) or a failed ABS module pressure sensor.

After hours of reading, it seems that these ABS modules appear to fail on the rear right (G44) ABS wheel speed sensor (very low speed output relative to the other three ABS sensors) but in my case it was an electrical problem - power. After a MoT fail on an O/S/R wheel bearing I had already replaced both rear wheel speed sensors and both rear wheel bearings. Unluckily for me I fitted a brand new bad wheel bearing (broken magnetic pattern) from SKF before I even knew how to check it with magnetic film.

I've seen a few posts where the problem was loom deterioration i.e. broken wires / corrosion (typically within the first metre from the ABS module plug) so I have investigated / hacked into that part of the loom and I eventually de-pinned the ABS module connector to isolate every single connection with test leads. That (bad connection, continuity) wasn't my problem.

I've also seen some strange posts where people had fixed a similar problem by cleaning their fuses. This didn't make any logical sense to me but I did it any way with no change in output.

My first clue was when I swapped the two 433 relays in the engine bay fuse box and saw different outputs in the VCDS graph. I bought a second hand engine fuse box from eBay and replaced the two 433 relays, the 458 relay, and any fuse with the same value from the donor (because why not). To my surprise the rear right G44 wheel speed signal improved, indicating that I had some kind of electrical power problem.

So I cleaned all the earths in the engine bay (sanded, copper greased, replaced with stainless nuts and dome nuts). There are about 5 earths near the N/S/F headlight and one in the N/S/F scuttle. I don't know which ones were the problem - I was going for broke at this point - but at least one feeds into the ABS module. That was the fix - power to the ABS module. All wheel speed sensors then read similar values when brake discs rotated with a few kicks.

So if you're having ABS wheel speed sensor problems, if no one else can help, and if you can find them, I would recommend cleaning all the earths in that area because that's 0.5 hours and some grazed knuckles vs hours and sanity tracing your loom.

Hope this helps the next person along - it damn near killed me!