ABS light has come on.

I assume it must be one of the sensors, but is there an easy way of finding out which one it is?

 

Some models have readable diagnostics. See workshop manuals available on here. Sadly the 03 cars seem to specifically not have this feature. I went mad trying to find the non existant connector block. When my ABS light came on I ended up taking it to Scoobyclinic and they found OSR sensor kaput, replaced, cleaned all other connections and now all seems ok. Beware sensors are expensive. I believe the most common fault is crud on the tone rings on one of the wheels rather than a dud sensor.