Even as a VW specialist I hate these FSI engines. They're a money pit.

The NOx sensor is a common failure and is generally hard wired to the NOx control unit. There is also a software update which I would of thought the dealer would have applied when changing the sensor. Post cat sensor is part of the NOx sensor.

The rad fan fault code is also common on the mk5's. One of the fans will have stopped working - a new fan will fix it but the remaining fan is perfectly ample. It just runs at full speed more often. Personally I'd ignore this one if the customer will too.

The only faults that will put it into limp are the throttle and fuel pressure so I would be checking the serial data and scoping. I've also replaced engine ECUs on the FSI but they usually give more pronounced faults like failing to start when ever they fancy. Check for wiring breaks near to plugs on the items with faults - seems to be getting more common.

Matt