Brake, Air, and VAGCom

Hello,
I'm having a small problem, and maybe someone here can offer some advice. I haven't really found anything helpful using the search function.
'I had to replace the rear brake calipers on my G4, which has ABS but no ESP. For years, I've been using a homemade brake bleeding system that connects to a tire valve and then pressurizes the reservoir attached to the master cylinder. You just have to refill it occasionally. It's always worked perfectly until now. Today, even after three bleeding cycles, I still have air in the system. The reservoir hasn't emptied, so it shouldn't be air in the ABS unit. Or is it? And if it is (which brings me to my question...), how do I get it out?' I have the full VAG-COM software, and it seems there's a procedure for this, but the explanation is very brief ('Measurement block 001: Press the brake pedal, open the bleed screws at the front.' Do you open them first, or brake first? And does the bleeding device need to be attached to the reservoir and apply pressure? Block 2 says 'brake 10 times and close the valves.' If I understand correctly, you should brake 10 times with the valves open, and then close them again. Then the storage container is definitely empty...
And you're supposed to repeat the whole thing x times.
Perhaps someone can be kind enough to explain it briefly. Thank you in advance.

When performing repairs like changing brake pads, it is not necessary to use a diagnostic tool to bleed the brakes. The diagnostic tool process is only necessary if the reservoir was empty, or if you are replacing the master cylinder, ABS valve body, or pump – to bleed these components, not the lines or calipers.

The text that VAG-COM provides during the process is almost exactly the same as what the genuine tools display. I know they are not very detailed, but they are only meant as a reminder, and not as a replacement for the repair guides.

-Uwe-
VAG-COM Author.

If there's air in the system, it can take quite a while for it to completely disappear. So, always make sure to pump and refill properly. Next time, you will surely be more careful.

*excavate*
(because it probably comes closest to the topic of my problem).

My Ibiza 6L with...

Address 03: Brakes.
Protocol: KWP2000.
Part number: 6Q0 907 379 AQ
Component: ESP 8.0 front
H04 0002
Encoding: 0002347
(312 series front unit)

Even after thoroughly bleeding all the wheel brake cylinders (at a reputable workshop), the brake pedal still feels somewhat soft. When the engine is running, it depresses about halfway towards the floor with moderate pressure, only becoming completely firm at the very bottom.
The behavior of the brakes during driving seems normal to me, especially during regular braking, just like I'm used to from the Polo (with its 288 mm system).

However, the Polo only has ABS, while the Ibiza has ESP with brake assist, which initiates full braking when the pedal is pressed quickly and partially, as if the driver were braking fully themselves.

The spongy feeling in the brake pedal, in my opinion, most likely indicates trapped air somewhere within the hydraulic unit, which cannot be removed through normal bleeding procedures (at the reservoir and wheel cylinders).
Does anyone know the exact procedure for bleeding the system mentioned above? EPS with VCDS?

Is the answer already here?
/viewtopic.php?t=529&highlight=esp+entl%FCften


Could the HBZ (hydraulic brake booster) also have a problem with its seals (damaged bellows)?
Before my purchase, the car likely sat at the dealership for a year or longer, and according to the warranty booklet, a brake fluid service was performed as part of the pre-delivery inspection.
When bleeding the system using the pedal (instead of a refill pump on the reservoir), it is supposedly possible for the piston seals in the HBZ (hydraulic brake unit) to fail if they are moved within cylinder areas that have a rough, corroded surface, areas that are normally never used. But then, I think it should be possible to slowly press the pedal all the way down without it becoming completely hard at any point along the way?