I have a 2000 model 1.0e and the abs warning light comes on when I reach 20 mph. It goes out when the ignition is switched off and then on again.I have checked with a code reader and it says abs power unit fault. I have proped the front end and 'driven' up to and past 20 mph and NO LIGHT. If it was the main unit fault wouldn't the light still come on?

I suspect that it is a wheel sensor, how can I check??