ABS light

[Ben]

My ABS lights on and my MOT is getting dangerously close! It's been on since I took both the front sensors out and put them back in for a hub change. The sensors are around £45 each though

Firstly is there any way of checking the sensors?

Secondly is there any reasonably simple way of making the light come on when I turn the key but then go off as it should when the engine starts?

Thanks