I have a 2015 VW Jetta tdi (AdBlue). Can I use a new long neck funnel to add it or do I need to buy a special refill bottle?

SOURCE: how to replace a coolant temp sensor on a 2001 vw jetta 2.0

Yes it is that easy. It should be a 4 pin connector located on the transmission side of the engine head in a plastic flange. Best is to wait for the engine to be cold. Unscew the radiator cap to relieve pressure but screw it right back on. On the 2.0L engines when you unclip the coolant sensor little or not coolant loss will happen if you do this. Just unplug it, pull out the clip, pull out the sensor, and the seal which sometimes stays stuck. Install the new sensor with a new seal lubricated with some coolant, make sure it's well seated and reinstall the clip. The sensor is well seated if the clip fits right over the top, just make sure both sides clipped into position. Replug it fill the coolant with VW original coolant mixed 50-50 with water if needed and done. If you have a fault you might need a scanner to erase the check engine or fault in the cluster.

What's the reason for changing it? Eratic temperature readings?

SOURCE: transmission fluid check on a vw jetta tdi

Never ever bring a jetta to a volkwagen dealer. They will bend you over and rape you.

All you have to do is remove the top plug with a hex wrench.

SOURCE: 2006 vw jetta tdi service engine light reset

With the key in the ignition (but not turned), press and hold the Odometer Reset Button on the right hand side of the panel. While still holding that button, turn the key (although not far enough to start the engine) and then press and hold the Minute button on the left side of the instrument pane(if pressing doesnt work try turning the knob clockwise until service light has gone off and skip the pressing)l. Release both buttons at the same time.

SOURCE: p0106 map sensor code on tdi

02 jetta map sensor code p0106 and faulty boost sensor code p0238

SOURCE: vw jetta 2003

Seems problem exists more so from the recall to replace the so called Faulty Ignition coil. I had mine replaced by Recall Notice. I packed up the car and headed north for the weekend - 1st drive after coil replacement approx 190km - upon return for the weekend another approx 80 km the engine lite came on. Returned to my dealer here in Toronto and they assessed the Cat trouble. Researched Cat converters - Dudes and Dudettes. This Cat trouble is bogus- Cats should out last 2 car's unless your power is way down and you can't keep it running - and noticeable loss of power would ever a cat be required to be replaced. This is to get you to come in and spend your money with them. Car care has become another great business of scamming legally. You the ****** are always taken for non-required service. Research and you will always be ahead of their game. I'm also suffering this habit of engine lights coming on. I'm thinking of the investment to an ODT2 unit and keep it with me for such occasions to clear the codes and await it to return. Which I'd expect will be some time again. VW's are made for the autobaun - meaning hard driving. Don't let some whistle head talk you into spending more then you need. Cash flow management. Cheers.