Well....

 

Replaced the brake shoes and adjusted the handbrake and the car was driving fine for a few days. 

 

Then I took it for an MOT (handbrake and emissions after a leak in the front of the flex pipe).  It passed.  As I was leaving the estate on which the test centre was the abs sensor light came on and now is on permanently.

 

I didn't even know that the car had abs.   It still brakes fine.  There are no electrical connections to the back brakes or front that I have seen. 

 

Any thoughts that might help on this?

 

Cheers

Justin

 

 

Glad you finally got your MOT. 👍

Check strip fuses in fuseholder above battery, I think ABS will be position no. 4 in your car. Cracking of the metal strip often causes ABS light.

 

Could also be a wheel speed sensor (which point at the inner face of the wheel bearings), but most often it's the strip fuse. All UK market Fabias have ABS as far a I'm aware.

 

Edited 4 July, 20241 yr by Breezy_Pete

Could it (the wheel speed sensor reading) be caused by the rear shoes grabbing a bit at the hub?  That was what I was experiencing when I fitted the new shoes.  One wheel span perfecly the other needed some effort to turn when the handbrake was off.  

Edited 5 July, 20241 yr by jpadie

What you have described sounds more like being a physical "thing" with that wheel's brake shoes, like not be allowed or forced to centre or something else concerning the springs, pivots hold downs or wedge adjustment/condition.

 

The ABS system just modulates the fluid flow to the 4 wheels in response to one or more locking up.

Sure.  I will lift the car again and see whether the shoes need adjustment.  Seems always to need doing on a day I have to get to an airport.

 

If the shoes are grabbing then the wheel may spin slower when driving.  I.e. there could be lots of micro skidding on that wheel.  I'd expect the hub to be very hot in that circ though.  And a quick drive to Screwfix and back just now had both hubs at about the temp of Luke warm bath water.  

 

I'm suspicious because the abs light is about the only thing not to have flashed up on the dash of over the last year.  Then I change the brakes and it's fine for a week.  Then off to the MOT (where it was on the rolling road) and suddenly it's complaining.  

Check the fuse, please!

Sorry @Breezy_Pete - I had checked strip-fuse 4 and it's pukka.  

If you're certain (they sometimes crack so imperceptibly that only undoing the nuts makes it evident when they fall into two pieces); then I'd imagine you've knocked and damaged a rear sensor or wiring to one whilst doing the brake work. Check the side you changed the cylinder on first.

Did you remove hubs/bearings while changing shoes, or work around them?

have lifted the car and the wheel spins well enough.  so next stop is to check the wheel speed sensors.  unfortunately I can't find my scan tool.  

Just now, Breezy_Pete said:

If you're certain (they sometimes crack so imperceptibly that only undoing the nuts makes it evident when they fall into two pieces); then I'd imagine you've knocked and damaged a rear sensor or wiring to one whilst doing the brake work. Check the side you changed the cylinder on first.

Did you remove hubs/bearings while changing shoes, or work around them?

did both sides, cylinders and shoes.  I didn't remove the hubs.  

 

Just to salve your conscience I will unbolt the fuse and double check.  i did give it a good scrubbing with a brass brush and some Isopropyl alcohol.  

 

No, if you've been that thorough with the strip fuse no need to do more. It's just such a common cause of ABS light on this platform that it's not worth doing anything else first, unless you have fault codes pointing at a speed sensor.

Find that scan tool.

Check the wiring near the sensor connectors, could easily have been damaged while freeing wheel cylinders/brake pipes/bleed ripples if you weren't aware of their presence.

1 minute ago, Breezy_Pete said:

Check the wiring near the sensor connectors, could easily have been damaged while freeing wheel cylinders/brake pipes/bleed ripples if you weren't aware of their presence.

yup - will do.  

took the fuse off and checked again under a magnifying glass.  all is well there.  

Also, you found a loose bit kicking around in the drum at one point, I seem to remember? That could have collided with sensor head, perhaps?

Just now, Breezy_Pete said:

Also, you found a loose bit kicking around in the drum at one point, I seem to remember? That could have collided with sensor head, perhaps?

that was the adjuster armature.  it. had come off the spring and been thrown out of its housing.  

how would something inside the drum dislodge the wheel sensor?  

Because the wheel speed sensor pokes into the drum through the backplate, to point at the inner face of wheel bearing.

 

The rectangle just below the wheel cylinder in this image. (Ignore the red-ringed bits, they were illustrating the 'glide pieces' which the shoes rest against.)

ah!  I did not see this as I never removed the bearing, makes sense though.

I've got a 36mm thin wall medium depth 12 point socket somewhere that I've used on other VAG cars.  Hopefully that's the right one for the fabia too! 

Probably easier to undo and withdraw the sensor from the outside/rear of backing plate, and examine that way.

 

4 hours ago, jpadie said:

ah!  I did not see this as I never removed the bearing, makes sense though.

I've got a 36mm thin wall medium depth 12 point socket somewhere that I've used on other VAG cars.  Hopefully that's the right one for the fabia too! 

 

Just a passing comment now that you have mentioned that you have a 36mm 12 point (BiHex) socket, that you have probably used in the past on the front hub nuts, if the rear hub nut is the same for rear drum brakes as for rear disc brakes, then it is a 30mm 12 point (BiHex) socket that you will need if you plan on ever removing the rear hub(s).