Untraceable ABS issue.

[Jonny54]

Alright Ladies and Gents.

Last june i bought a 2005 A3 with the ABS light on. I was intending on fixing it but the warning lamp stopped flashing up for 6 months or so until recently and its come back.

MOT is in a few months so i need to get it sorted really.

Its come up as the rear nearside wheel speed sensor, but the previous owner said he had replaced the sensor, the bearing and hub, etc. Since my ownership i have replaced the brakes on the rear.
He also said he had tried swapping the sensor from the other rear wheel but the fault remained.

Any idea's gents what it might be?

The only thing i think is it could be a break in the cable from the ABS module under the bonnet, to somewhere along the car before it hits the sensor..? What do you think?

Thanks Jonny54

 

[SmithyAG]

Sounds more like wiring if the fault does not follow the sensor.

I have one on my car, ABS pump implausible voltage or short to ground. It rears its head whenever I've been near the fuse box, or just had it washed, and then disappears again for up to a year at a time. It is most likely a corroded ground on mine under the fuse box or a duff fitting fuse/water in it somewhere. I'll be damned if I can find it, and the warning never stays on long enough for me to figure out if anything I've done has fixed it.

 

[Mikemc]

get it scanned with VCDS and then post up the results then it will be easier to advise you

 

[Jonny54]

Thanks gents. I will get the full info and get back to you.

The cable is only a cheap job if its that to replace!

 

[s3_sid]

have you checked what the connection onto the abs pump is like i have seen them get wet and get corroded pins not on 8ps but other vag stuff i was searching for ages then found it

 

[Jonny54]

Oh wow. Ok man, thanks. I'll check that!

 

[Mikemc]

You had it scanned yet? We're you located?

 

[Jonny54]

Im going to get my friend to scan it for me at the beggining of next week. Then i shall report back to you guys.. Im Located in Lincoln at the moment!

 

[MrLapou]

I'm in Lincoln too and have VCDS.
For any involved repairs I'd recommend this indy... Just Audi in Outer Circle Rd.

 

[preecey75]

Have you had the problem solved yet!? I'm having such a hard time with my ESP/ABS light at the moment, AND my MOT is up TODAY!!

 

[makster1978]

same here I have replaced both front abs sensors and now my left front locks up at slow speed garage said traction control is trying to kick in buts its a 99 a3 without esp,

 

[makster1978]

changing the front right abs sensor out tomoz I have scanned it and its coming up front right sensor intermitant,mot was today and drove it there with the fault it only failed on this,car was locking up front left every few seconds at slow speed even tho the faults on the right wheel,iv previously swapped the sensor but must have bought a duff,driving me crazy this problem

 

[freegeek]

I also have an intermittent abs/track light coming on, VCDS pointed to a problem with the right rear sensor, changed that and the problem remained, I just bought a new hub in the hope that it solves the problem.

 

[makster1978]

I changed my sensor with no joy.turned out mine was the wiring loom for the front right sensor someone in the past had taped it up just before it goes into the wing I spotted black tape once I peeled it all away bingo both wires were touching shorting it out,after doing a clean repair I deleted the error code and did another scan and the faults vansihed,I don't think buying a hub will sort the problem m8 the abs rotor what spins giving the sensor a reading is fixed to the axle and changing the hub wudnt solve that problem I could be wrong tho I no the front ones are a axle swap if they break,id give your wires a good check around the suspention look for insulation tape etc for a botch repair,also make sure the air gap between the sensor and abs rotor is 2 mil max,the Bentley manual says 0.3 mil butt that's a bit hardcore considering over the years the rust they gather I ended up cleaning all 4 rotors and replaced all 4 sensors at 2 mil,i had a complete nightmare with mine till I found the broken wire but all sorted now

 

[freegeek]

I don't think buying a hub will sort the problem m8 the abs rotor what spins giving the sensor a reading is fixed to the axle and changing the hub wudnt solve that problem I could be wrong tho

Pretty sure its on the hub on the rears, otherwise that's £26 down the drain.

 

[freegeek]

I had a look at the wheel speeds with vcds tonight, wish I had done this before buying a new sensor.

The first trace is with me driving the yellow trace is the one with the implausible signal, comms crashed after a few seconds of driving so the trace is not very long.

I thought it may have been a bad connection making and braking from road vibration so jacked up the rear and spun the wheel by hand and am getting the same noise, so I am pretty sure it is the hub/abs rotor.

 

[freegeek]

Problem solved with the new hub. You can see that the old magnetic strip on the old hub was starting to disintegrate causing the erratic speed readings.

Changing the old hub was pretty easy with the M18 spline bit a long breaker bar and a pipe extension, it needed a bout 5 feet and all my weight to break the old hub bolt free.

All in the job took 45mins, would have been a bit longer if I hadn't just changed the discs also a couple of weeks ago.

The manual says you need to remove the brake calliper mount to get the disc off but you don't unless there is a build up of rust on the inside of the top hat part of the disc, which I had to do first time but not this time with the new discs.