ABS light illuminating

[brianb]

Hello,i have had my ABY coupe now for over a year and have not really had any trouble with it until recently.Most times i go out in it now the abs light comes on(also the diff switch light at the same time),it only does it when boost is coming on,and then it usually goes out after a few seconds.It only does it a couple of times per time i am out in it.I have also noticed that the abs sometimes cuts in at slow speeds when there was no need for it.I have had it on various scanners and no fault is being shown.
Any ideas?

[newsh]

Almost certainly dirt on the wheel sensors.

[brianb]

how big a job is it to clean them?

[K Simmonds]

To do all four properly will take about 2 1/2 hours or so, as you will need to undo the all hub bolts and lower ball joints. If you do this remember to replace the hub bolts and torque them up correctly. Alternatively you could try spraying loads of brake cleaner in between the CV joints and hubs. Just a thought but have you had a hub off recently? ie to change a wheel bearing. Quite often this will be the offending corner as it is easy to get cr@p on the speed sensor.

[newsh]

If you can get the sensors out you can try an airline down the hole whilst spinning the hub, you need to set the clearance just right when you put them back in, the audi way to do this is to fit a new plastic end cap and push it in till it just touches, I've pushed them in and just pulled them back a 1/2mm and that works.

[QuattroFever]

could be the non return valve for the diff. lock under the rear seat. It's the little black and white thing that looks like a spinning top.

Try this first as its a only few pounds for a new one and will save you all the aggro if you don't need to change wheel sensors.