[Solved] Error P0401 VW Caddy 1.9 Tdi 77KW 105km BLS Too little exhaust gas flow in EGR

Hello.
I am the Owner of the recently Vw caddy 1.9 tdi 77kw 105km with the BLS engine.
After the purchase, returning home after 30 km, I got a flashing indicator of glow plugs. After turning off and starting the car, it went out and then it appears again and it would not be too easy, it turned on the orange engine check.
After attaching it to the computer, it showed error P 0401 for low exhaust gas flow in the EGR-flue gas recirculation system.
I exchanged egr for a new original Pierburg for a week he was calm again as the mantra returned the same.
I am asking for help, what I am still in this layman, maybe someone has to deal with such a case.

First of all, you need to understand how Ecu measures the flow through EGR. In fact, it calculates / guesses. Ecu measures the flow of fresh air right after the filter. This is done by a flow meter. And now Ecu has a fixed air flow for specific revolutions, atmospheric pressure, fuel dose and inlet pressure (after turbo). When the load is incomplete and even small, it closes the throttles and opens the EGR so that the flow of fresh air falls to the assumed level. On the basis of the difference, since the engine did not get fresh air, it selected the missing amount from the exhaust. The error for low flow is caused by too much fresh air and despite 100% EGR opening does not reach the assumed level. The problem may be related to the flowmeter (damage to this side is rather rare because it is more likely to be understated, but it may not be that engine that happens to be replaced by the one needed) exhaust return channel clogged with soot and crumb (together with EGR cooler), blinded EGR, EGR control does not work or problem with the quenching / quenching flap.

I will add it does not lose the power it collects well, it does not kick anything Nothing can beat it beautifully fires on a cold and warm engine. Can there also be something else snagged?
And that's the reason? As the new one was replaced, the old man had a lot of crap on himself and in the place where he was screwed. You can not say anything clean, you do not even know if it's killed.
And if there is a damaged flowmeter, will not it show up under the computer?

Added after 3 [minutes]:

And one more question; Do you need to adapt a new EG after replacing because it has not been done ...

Hello, I am coming back to the subject all the time there is error P0401 for a small flow of exhaust gases in egr.
I could not stand it and flew by cleaning everything until I came across plugs on the exhaust in the cooler egr at the inlet and outlet.
And hence the question why could someone do it?
I am asking for advice and help.

One by one, cleaning the mechanic, starting from egru in turn into the cooler, Egr found a blind pipe at the inlet and outlet of the EGR cooler. And the reason for the blinding was the creation of the slip in the cooler egr where there was a play on which the whistling and flue gas was created. Mounted new and car as needed.