I can't seem to think cleaning a TDI engine bay would be any different than cleaning a gasoline engine.
I would try to remove the engine cover first, clean the engine cover off the car, and then make sure don't let too much water get in touch with all the electrical connectors. Let the engine bay dry up a little bit before staring the engine too.
If the engine cover is not removed, the three holes where the three bolts are might collect water underneath the caps.
Do remove the engine cover. Cover the alternator with a plastic bag. The cleaning chemicals aren't good for it. I would not use a pressure washer since it can damage wiring and force water where it doesn't belong. A hose on gentle pressure is fine. Then blow out water from any plugs you can see or standing water.
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