You all probably know to replace your black coolant sender with a green one. But after a couple of years, I had a weird failure of the replacement green, probably chinesium, sender.
The car had lost some of it's usually excellent MPG, so out with the VCDS.
The temperature gauge was doing it's thing fine, but with a hot engine, VCDS was reporting the engine coolant temps were saying stone cold.
The temp sender has four pins, basically it is two identical temp senders in one unit. One sender runs the gauge, the other goes to the engine management / fueling map.
Changing out the sender got the temps right in VCDS, and fuel mileage improved about 5 mpg. Or 4mpg for you Occidentals.
The plug was full of coolant, as was the bust sender, fortunately the coolant hasn't migrated up the wiring to the instrument cluster, lucky there. So the brass part of the sensor must have cracked.
Stock up with a couple of genuine vw "O" rings for the coolant sender, as the aftermarket ones are utter gash. Don't ask how I know, G12 is not cheap.
