My ABS light came on intermittently and then became permanently on. I checked the wiring under the fusebox (as per the threads on this forum, did find a bad dodgy connection) but it wasn't the problem.
I thought that by unplugging and checking the resistance of each sensor I had eliminated the sensors, they were all 700 ohms......but this is not so. This mistake led me to waste time checking the wiring from fusebox to ABS module etc.

So, how to check the sensors.

1. Un plug the sensor (the rears have a red clip that you have to slide back before you can squeeze the plug and disconnect it) and make up a couple of wires so that you can effectively "reconnect" the plug but you now have conductors that you can put a multimeter on. I used short lengths of wire with a bullet connector on one end that I squeezed up to make good connection on the pin (male plug) and a piece of copper solid wire on the other end just the right size to fit the socket ( female plug).

2. Ignition on, meter set to 20 v DC you should have about 8.5 V across the sensor, spinning the wheel makes no difference. This effectively checks the wiring from ABS module to the sensor.

3. Ignition on, meter set to 2 v AC you should have 0 v AC (or there abouts), spin the wheel and you should have about 0.5 v AC, if it remains at 0 v the sensor is faulty.

4. Replace faulty sensor and drive the car, ABS goes out when you hit 15 MPH.


Incidentally, although the front sensors are handed, it's only the two brackets that are handed, the cable/sensors are identical. So you could fit a left hand sensor to the right hand side by swapping the brackets over.

Hope this helps someone out.

 

Rodger, thanks! This helped me quite a bit. I had already started checking the sensors in the naive way, with sensors disconnected. This obviously does not work.
My multimeter apparently responds different from yours. In the AC mode my multimeter does not give sensible readings (constant 22V, wheel spinned or not), but the DC reading is about 9V and alters with 0.5 V when the wheel is turned, except for the right front wheel so I guess that one has a broken sensor.