my abs light comes on with (!) flashing after about 10/15 min of driving, been told it could be my ABS sensor, my mate said i could test the sensors with a volt meter by doing a resitance test, so thought i would give it a go, i jacked the car up unpluged the sensor, put the volt meter on the plug an spun the wheel, the 2 front sensors fluttered up an down when i spun the wheels but both back 1's just sat on the same reading, the resitance didnt change, i think i seen something somewhere about there being a ring that you can change that the sensor reads off, is this right??? im used to working on vauxhalls an they have teeth on the cv joints which the sensor reads off