Just another quicky on this .fault says intermittent sensor failure right hand rear. by the way i have a 2007 1z3 octavia vrs. i have disc brakes all round so is it better to replace the rear hub on its own(is hub the right term?) and replace the abs/ speed sensor or not? does anyone have the correct part numbers for abs and hub?

More than likely the rear wheel bearing at fault. Change the bearing and all should be well.

I would first take the disc off and remove the wheel speed sensor and clean it with some brake cleaner and see if this clears the fault. If not I would expect the sensor would need to be replaced not a hub or wheel bearing.

cheers guys will clean it first.  how would the wheel bearing bring the sensor light on???

It wouldn't... The inside of the hub has a 'ring gear' which the sensor uses this may need a clean as excessive brake dust can alter the magnetic readings. The wheel bearing has no influence on the sensor at all

The sensors very rarely go wrong. What normally happens is rust builds up on the pick up on the bearing and messes about with the signal. You can take it off and clean it, but tbh when bearings have bee run they don't like being slackened off and re torqued much. Better off doing the job properly first time.

It wouldn't... The inside of the hub has a 'ring gear' which the sensor uses this may need a clean as excessive brake dust can alter the magnetic readings. The wheel bearing has no influence on the sensor at all

So if there is movement in the bearing this doesn't alter the air gap between the pick up and the sensor?

You can see the pick up here on the bearing. As far as I'm aware is not a seperate part. Even if it was the bearing would still have to come off and quite often comes apart on removal. Rust usually builds up in and around it and distorts it so it gives incorrect readings hence bringing the light on.

Been changing them for years for the issue.

Problem sorted and guess what! It was the wheel bearing so new one fitted plus new sensor jobs a good un!.