Abs

[Dolomite]

Hi
I have a MG ZTT CDTI,
When I start the car the ABS light goes on then off as it should, but when I brake the pedal modulates with the ABS ,
After a few times the ABS light comes on and ABS is disabled until next journey,
When a new journey is made the ABS light comes on and stays on until you drive over 7MPH when it goes out,
But when you brake the ABS operates again,
The Speedo works fine,
I tried to remove the NSF ABS sensor but can’t get it out,
Any ideas what it is and also how do you get the sensors out
Thanks
Darrell.