Last fall I was breaking my 6 for spares when a new engine fell into my garage and the car was brought back to life. As part of braking it I drained the brake fluid completely and removed the discs and callipers. After crossing my fingers and re-filling the system the brakes feel absolutely fine, but I noticed in the car park after work when playing in the snow, that my ABS no longer works. My wheels are locking up!

I suspect this is related to me draining the system, can the ABS "unit" be bled on its own? Or should I suspect more expensive repairs?

By the way, the only brake warning light I get is the one stating my brake pads are worn, and I have a new pair waiting in the garage.