ABS Wheel Speed Sensor "Tone Ring" problem

[SonicDeathmonkey]

So my ABS has been kicking in on and off at low speeds. I think, but am not sure, that I've got some wheel speed sensor issues, but vagcom shows nothing.

I found this picture online. It's not audi, but different is the setup on an S4?

 

[aragorn]

If its triggering randomly at low speeds its probably a corroded or perhaps even cracked ring, and ye, its pretty similar to your image.

If you have vagcom, you can connect to the ABS controller, and open up measuring blocks, which will show you the signals from each wheel, If you drive along VERY slowly you might be able to see which one is dropping out, as it will likely stay at 0 longer than the others or might jump between a speed and zero.

If you go much faster than about 10mph vagcom will disconnect from the ABS controller, so you really need to keep it to just crawling along.

 

[SonicDeathmonkey]

cheers. i've noticed vagcom dropping out. didnt know it was speed related. will try it this weekend.

Any idea what cost I'd be looking at to get a pair of wheel sensor rings? plus fitting? would I need new sensors too?

 

[Geeman]

Mine was coming on a low speed as I was braking, about 8mph.

I replaced the sensor (not the ring) and now it's perfect!

Hardest part was getting it in the air high enough on axle stands to get underneath it to place the grommet back in under the seat access point!

 

[aragorn]

Well i guess common sense is needed.

The rings are part of the CV joints. You basically have to change the CV. The rear CV's on quattro models seem to be prone to the ring cracking, meaning its loose on the shaft and moves around, causing the problem.

When i got our car the rear had no signal and i stupidly dived in and changed the sensor first rather than properly investigating, turned out to be a shattered ring (it was in two halves lol) and i ended up getting a spare driveshaft from ebay and swapping it over.

I'd use vagcom to identify the corner, then once identified, you can look at the ring. If the ring looks fine and isnt corroded or owt, then replace the sensor. Otherwise, replace the ring!

 

[SonicDeathmonkey]

Well, I am off on holiday on two weeks. Think I will leave the car with a local garage and ask them to have a look. Hopefully they will know their onions!

 

[tazzy baby]

Sorry to jump in on this but mine comes on when i go over 60 anything below it stays off but i do get a bit of a fight off the pedal when i try to stop any ideas