Hello all

 

I have had a wheel speed error since changing the rear brake shoes a couple of months back.  Diag tells me it is rear left.  Changed the sensor this morning but the error persists.  The cable inspects fine.

 

Is there something I could have done inside the drum to cause the problem?

 

Cheers 

Justin

 

Could have damaged the reluctor ring on the bearing, check that and the gap between that and the sensor too. Also sometimes have to remove all corrosion from where the sensor sits as the gap can get too large and cause problems

Thank you. 

 

Is there any way to inspect the bearing without dismounting it?  I did look at inspecting it when I changed the brakes but found that I could not get the cap off non-destructively.  

 

 

I've ordered a new bearing and will fit it on Wednesday; and give the area a scrubbing in case it's debris (some of the glide plugs are missing, possibly something could have got in and created a deflection to the magnetic field).  Unfortunately I'm up against some time pressure as my youngest needs the car to take her test next weekend!  Fingers crossed that she can become the designated driver soon.

 

took the bearing off and it looks like the mag-ring was damaged.  new one is on and fingers are crossed.

 

Pretty sure the magnetic bit is inboard of your markings/damage. The bit I've scribbled in blue on:

 

Edit, nah, ignore, see following posts

Edited 26 September, 20241 yr by Breezy_Pete

you could be right, Pete! 

this is a photo of the new one.  it looks to me that the bit you blued is the outside of the race-bearing.  Although it's static (with reference to the hub) I think it is unlikely that they would manufacture the bearing itself with magnetic zones.  but who knows!

  

this other site seems to agree btw.  https://www.vweosclub.com/threads/visualize-a-magnetic-abs-sensor-on-a-v-w-wheel-hub.37149/

 

the proof is in the pudding perhaps - I will take it out for a spin in a couple of hours. 

Edited 26 September, 20241 yr by jpadie
photo in the wrong place.

Ah, I think I know where I was going wrong. The one I was comparing photos with was a front bearing, which looks different.

 

I think the following pic is a rear one, looking like yours:

 

 

 

 

Well as it happens I've taken it out and the abs error has come back.  Not sure whether it's just because it's a stored error or because a new bearing didn't fix the issue.  

 

So far new sensor and new bearing and when driving I can see that the wheel speed is being read.  So the cable is ok.  

 

Not sure what else can be wrong now !

 

Reset the fault codes and took the car out for a short drive.  Warning light came back once I hit 50kph.  Had a flight recorder going on the wheel speed sensors and they all measured within 1kph of each other the whole time.  

 

Brake fluid normal.

 

I've taken the sensor out and scrubbed the area again but I doubt whether that has anything to do with it!  

 

Car still drives fine of course.  But no abs.  And I doubt the driving test invigilator will allow my youngest to take the test with the abs light shining balefully! 

 

If anyone has any thoughts for investigation, I'd be grateful.  

Maybe failed ABS control module, common on Volvo 700 series. Break in circuit board. The Volvo uses similar set up.

Any solid way to diagnose it?

If you've replaced the sensor and checked the wiring for continuity back to the ABS module then you should try and get hold of a used module. I don't know if you need to remove the ABS unit to access the screws but the module should be separate to the ABS unit. It's a long time since I had to do this.

Thank you.  I'm not sure where the abs ECU and pump are mounted in a Fabia but will see how far I can scoot under the car tomorrow morning.  The wiring looks ok and is providing solid enough input to the ECU so that Delphi reports continuously   The ECU is reporting solidly to OBD.  Best I can come up with at the moment is an intermittent break in overly brittle wires.  Replacement abs units seem to be more than I paid for the car but it could be that I need to visit a breakers yard. 

 

 

I replaced a section of wiring that looked very slightly compromised and then really hoped the problem would be fixed.  

 

It wasn't. 

 

The abs light comes on after 2-3 mins of driving and around 30mph. 

 

Next step is checking the wiring from the  ECU end but I have no idea where it is mounted.  Does anyone have a wiring and connection diagram and know where the ABS ECU is mounted?)

 

Cheers

Justin

ABS module is just below engine ECU.

Can look up wiring info tomorrow if you like, but it's probably in the circuit diagrams contained here:

 

Thank you Pete.  V kind 

Is there a sheet or hint for accessing the rear left wiring loom?  The abs line goes into the chassis quite shortly after leaving the hub.  Is the wiring loom accessible from the inside of the cabin?  

Lift up the rear seat squab, and you'll see it coming up and in there. From there I think it heads along the bottom of the door orifices, under the trim.

 

Another user a few years back (7!) discovered a splice in the (rear ABS) wiring somewhere under the rear door, which had corroded due to 'traditional' water ingress through carrier seals. Can't remember the username just now, but there are such splices here and there in the wiring looms, where wires are 'crimped' in with others and then taped over.  More vulnerable than continuous insulated wires.  I may remember as I wake up more through the day.

 

 

Edited 29 September, 20241 yr by Breezy_Pete

Google to the rescue "skoda fabia abs wiring loom splice" found it, no sweat.

Halfway down this page: ABS Warning light - Page 3 - Skoda Fabia Mk I (1999-2007) - BRISKODA

 

Thanks again Pete. Will need to dig out my trim tools it seems.  I had terrible mould in this car until I siliconed the door internals so it's not impossible that corrosion is a culprit.  The wiring diags for earlier models show a junction there as it goes into the loom but a splice would make more sense from a fit perspective and a greater likelihood of an intermittent failure (the wheel sensor continue to report to the ECU even once P00290 has fired). 

 

I've learned something important too.  Apparently there are wood pigeons in car seats these days!  Who knew?  

no splicing or connector in the rear cills .  the LHR sensor comes up under the seat,  snakes to the door cill then traverses to the RHS, meets the RH loom and goes forward; again no obvious splicing but I have not opened the loom to be definitive. I've lost it at the seatbelt anchor and am now looking to see whether there are any online resources that show me the path it takes.  in the wiring diagrams there is another connector block but I have not yet come across it.  perhaps near the drivers' knee fuse box?

 

The connector is at/through the firewall, pretty much impossible to access cabin-side and a bunch of work to get to in scuttle on engine bay side. 

 

 

 

rats.  ok.  

I don't think continuity testing is going to be useful sadly.  whilst the error happens every time without fail, the sensor continuously reports data so there must be some more or less persistent connection.