[cuppie]

That sounds like dead wheel speed sensor, or failed ABS module.
"Light comes on after vehicle moving" generally means "one wheel speed sensor transmits no signal." This problem has nothing to do with the brake hydraulics.

Need to scan the ABS module, and post fault(s.)

 

[cuppie]

thanks, I understand that separate system, but doesn't brake fluid run thru block that is attached to abs module.

Yes, brake fluid runs thru the hydraulic unit. How else would the electronics regulate the brakes?

If there was air trapped in there, couldn't it cause a fault?

No. Only loss of braking power; low/soft pedal.
If, say, you have an air bubble trapped behind a valve, the brakes may be 'normal', until you hammer on them (read: ABS regulation, causing said valve to move, and dislodge the air bubble.) This will NOT cause a fault to set - it'll just be like you need to bleed the brakes again (soft/low pedal.)