Perhaps it could have something to do with the urea injection that the golf and jetta don't use? And if I'm not mistaken I don't think the Passat has a DPF. I'm not an expert nor do I know anything so don't quote me on this, just some suggestions.
No clue. I can't be related to urea injection because that is downstream. The Passat does have a DPF.
Here is the existing fuel routing.
I don't know why they would change anything here related to the engine so I can only assume it has to do with the internal filter housing routing. You must have at least a return and feed for the tank and obviously, a feed line to the engine and a return line. The fuel in the tank and the lines act like a heat sink for the fuel heated by the engine. There could be a line not visible.
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