Passat 3B V6 TDI: MSTG Failure?

Hello there,

We have a Passat 3B V6 TDI, and the problem is that the car stalled while driving and hasn't started since. The error memory shows two errors: 1. Engine control unit (ECU) defective, and 2. No communication with the engine control unit (or something similar).
My first thought was the pressure relief valve, but which one is it? And is it possible to have the control unit checked somewhere?
It was said that I should check at the STG (control unit) to see if there was power, and I assume they meant the 9-pin connector. On that connector, only pin 9 has power, regardless of whether the ignition is on or off. All other contacts have no power.

MSTG number is 3B0 907 401 C.

"Is the 3B0 907 401 J also compatible? What's the difference besides the fact that it comes from an automatic transmission and ours is a manual? Also, I believe the WFS (Vehicle Status Function) needs to be reprogrammed."

It's highly likely that this isn't the MSG (Message Service Gateway) or a relay, but rather the pump control unit, which means a new pump is needed.

But then why can't the MSTG (Main System Terminal Gateway) be read out? If the pump has to be replaced, it's going to be an expensive undertaking.

You must have gotten the error: '1. Engine control unit defective' from somewhere. If not from the engine control unit itself, where else? Telepathy?

That's exactly what I mean. I'm assuming that if it were the pump or the pump control unit, it would be readable from the engine control unit (ECU). However, the ECU itself cannot be read. I've sent it in for testing, and if it turns out not to be the ECU, then I've only wasted the €120 for the test, instead of the €1007 for a new ECU.

Okay, some news. The company that tested the MSTG says they couldn't find any errors. Now the question is, why isn't the MSTG readable? In my "old" Passat VR6, it was a faulty relay. What could it be in the 2000s V6 TDI? And can the fuel pump be tested separately?

Is all of this accurate? Well, it could be a wiring fault in the K-line or a defect in the driver within the MSG (Modular Service Interface). However, the power supply should definitely be checked when the system is installed. ESP (Electronic Stability Program) errors are read out via the MSG.

Where and how should I measure the voltage, and what options do I have now? I'm not completely inexperienced, but I don't necessarily want to spend more money at the workshop.

Okay, so, news: I had the car checked at a VW dealership for a diagnostic assessment. They also found a used pump from an A8 and installed it – the car is running again. The pump has a different identification number, but that can be adjusted in the MSTG (presumably a software or configuration tool).
Okay, so we'll just have to wait and see what happens now. The problem was that, after the pump was replaced, the MSTG (presumably a monitoring system) still reported an error with the pump.