Land Rover Repair: ABS problem, spinning the wheel, magnetic flux

Question
basically ive been conned into buying a 1996 3.9 V8i LPG discovery with faulty ABS, i was assured that "it worked" and that "the light just came on sometimes" well the ABS definately doesnt work!-it locked up on me the other day. we have taken it to a friend with a T4 and it just wont talk to it, it will communicate with the car when you click on any of the other diagnostic icons but not the ABS icon. he has checked the motor on the ABS and that worked, i got no readout when i checked for continuity on both the front sensors but assumed i had just not checked them properly (ive since heard that you have to jack the car up and spin the wheel to get a reading, is this true?) can anybody please help me as ive spent all my money on this car and really cant afford to go to  a main dealer to get it fixed, i just need to know what the fault is so i can get it sorted. many thanks in advance, Lee

Answer
Hi Lee,

Here's some comments I've collected on the subject of ABS sensors:

"The sensors are magnets surrounded by a coil, and are mounted close to an ABS sensing ring which revolves with the road wheel. These have segments, so that as the wheel turns the protrusions produce a magnetic flux in the sensor which is detected by the module. It is by comparing the frequency of these signals that the module can determine which of the wheels is about to lock up and will order the modulator to release the brake pressure to the affected wheel."

You could try spinning the wheel with ignition key in on (engine not running) to find a reading with your multimeter but I think it has to exceed 4.4 mph.  

You could also try testing for resistance: 950 to 1100 ohms

"Once you remove the sensor you should see the two contacts where the plug went. Put one lead on each contact while your meter is in the Ohms setting. This particular sensor is 50 Ohms, so you should read 50 ohms across the two contacts. If your meter doesn't move or shows an open, then your sensor is bad. If the reading is a lot higher than it should be, you have high resistance on the coil, and the sensor will need replaced."

The ABS problem is common with most LR owners.  I read somewhere recently that LR has finally fixed the problem with a redesigned ABS modulator.  (sorry, more $$$ you'll have to spend)

Seems the old model was replaced and the 'new' version has 'all the kinks removed'.  A few owners have said that it works but I'm still waiting for more feedback from other owners.

I hope this is helpful,
JohnMc