For many months my abs light would come on then go off again( 1995 1.9td) ! Then one day it stayed on all the time. Now its failed the m.o.t. ! When I phoned my local specialist , they said they would plug it into the diagnostic computer to indicate where the fault was for £25 . When I got there ,there was no computer. The mechanic stated that in his experience it was usually a front sensor gone , so he put it up on the ramps , removed the under belly cover , pulled apart the sensor plug where it joins the loom ,and then put his continuity tester ( ohmeter) on the two prongs of the plug going to the sensor . The reading was about 1000 ohms (okay ). He then did the same on the other side .Reading was showing no continuity , therefore the sensor was gone ! He quoted me £80 pound for a new one ! I told him I had seen them for £45 on ebay.I gave him £20 for his troubles , I then went home grabbed my meter , went down the scrapyard to a xantia that I knew was there , accessed the sensor and pulled the plug apart , tested the continuity , reading was 1000 ohms about , removed sensor from car , paid man £10 , fitted it when I got home . Hey presto light went straight out !!