In order to replace the brake fluid you do not need to home the HCU. You only need to home it when you are replacing the solenoid pack pr the master cylinder. Here are the instructions for bleeding.

1. Remove master cylinder reservoir cover, then fill reservoir as necessary.
   
2. Attach one end of a clear plastic hose to rear bleeder valve of the brake control assembly, then put opposite end of the hose into a clean container.
   
3. While depressing brake pedal, slowly open bleeder valve, until fluid begins to flow.
   
4. Close valve and release brake pedal, then repeat procedure for front bleeder valve.
   
5. Ensure master cylinder is full, then raise and support vehicle.
   
6. Bleed wheel cylinders and calipers using the following sequence:

1. Right rear.
   
2. Left rear.
   
3. Right front.
   
4. Left front.

1. Lower vehicle and check fluid level in reservoir, fill as necessary.
   
2. Turn on ignition and note pedal travel and feel as follows:

1. If pedal feels firm and constant, start the engine and recheck pedal travel. If pedal still feels firm and constant, continue procedure.
   
2. If pedal feels soft or has excessive travel either initially or after engine is started, repeat bleeding procedure.

1. Road test vehicle, make several normal stops from a moderate speed, then make one or two ABS stops at approximately 50 mph.
   
2. Ensure pedal is still firm and constant.