Passat AVG: Injection Start Control Error 17656

Hello!

We have a problem with a Passat TDI, model year 1999, engine code AVG, with an automatic transmission.
Mileage: 130,000 km. The timing belt was already replaced at 90,000 km.

The following symptoms:

After a short distance (maximum 200 meters), the ABS and ESP warning lights illuminate.
ABS control unit error code: 18265 - Load signal from the engine control unit (signal faulty).
Engine control unit error code: 17656: Injection timing control (function defective).

The errors can be cleared, but they reappear after a short period of driving.

Control of the injection start time in the measurement block showed:
Target: -1.3°
Actual: -3.7°
Engine temperature: 86°C
(Idle)

In the "Basic Settings" section, under "Injection Start Control".
It will be a diagram with a value A, a value B, and a shaded area.
displayed. The values shown result in a point on the graph that lies outside the...
hatched area.

We've now removed the timing belt cover, but we didn't find anything unusual.
I don't want to just mess things up now to bring the timing back to a normal level.
Why would the injection timing suddenly change overnight?
And does the injection start adjustment have anything to do with the faulty load signal?
What to do with the ABS control unit?
The curious thing is, it has absolutely no loss of power and no engine running issues.
To check for air leaks in the fuel system, we installed a transparent hose before the inlet. However, we were unable to detect any air leaks.

Maybe you have another idea?

Best regards, Rocco.