Help needed re 635csi

Can anyone help with this one?

A mate of mine runs a C reg 635csi auto on a daily basis. He doesn't know anything at all about cars and has paid a fortune for a new head and gearbox recently.

Now his ABS is playing up.

He tells me that usually the brakes are absolutley fine. However, occasionally the ABS light comes on and stays on and the brakes then pull to one side - or both 'grab' very violently. If you switch off the ignition and restart all is back to normal.

He also said that the light usually comes on when he's going round a corner or roundabout.

Any ideas??

I don't know anything about ABS and am hoping that am not going to have to tell him that he's in for megabucks again as he'll probably get rid of the car.

I think I can count myself extremely lucky where my 635 is concerned.  After over 2 yrs of storage I managed to go through an MOT with her with just 4 patches of welding required underneath, a tell-tale direction indicator and ABS indicator light on dash not working. 

The dashlights are jerry-rigged now so the ABS comes on only with the ignition light as the ABS system itself is in perfect working order, the light on the dashboard actually had no bulb holder or wiring to it.

 

The tester even commented that the brakes were exactly on book values when it came to the brake test, which was not only surprising when considering the car is 23 yrs old but one that has been stored too.

I can definately call myself very lucky with my car, I bought it for very little money, its one of just 4 on the Island, it has the second highest mileage but is in the best overall condition and is the oldest of the 4.

Being medically retired means I have plenty of free time on my hands so eventually she will look her best again.  Fortunately the previous owner threw huge chunks of money at the car, so all her main mechanical systems are in A1 condition.