Yo guys, I had exactly the same prob with my ABS.
Checked fuses, I've got PFC so i couldnt check diagnostics.. Checked sensors, everything. Ended up being a busted ABS module (The thing in the top right of your engine bay with all the lines running into it)
I got a replacement off someone on SAU for $80, and got a brake place to fit it (cost about $50).. Good as new!!
Just make sure to check the model number of the replacement before you buy it! Keep an eye out for wrecking R33 threads, and post a WANT TO BUY ad in the WANT TO BUY section
Good luck!