UrS4boy

This applies mostly to the C4 UrS4/S6 AAN but likely crosses over to the ABY and ADU. There are four coolant temperature senders of interest, each with its own unique purpose and function (be sure to follow the hyperlinks):

1. The ECU gets its coolant temperature signal from the G62 sender at the back of the head.

2. The Automatic Climate control gets its temperature signal from a separate sender located in a "T" at the back of the head. This temperature signal can be read through Channel 51 of the automatic climate control faceplate.

3. The multifunction temperature switch (MFTS) that sends the temp signal to the gauge cluster. This reading can be compared to the Ch. 51 reading to help diagnose whether you have a MFTS problem or a thermostat problem.
Note: this MFTS switch is supposed to have a rubber boot ("grommet") over the connector (Item 29 below) and exposed switch portion, as shown as Item 27 in the diagram below.

4. The after-run pump climate control switch - this is one that triggers the after run pump.

Bulletcar95

thanks for the info. my UrS6 comes up to temp fine in cool and warm weather, but wont come up to temp in freezing temps or stay there on long drives/long downhills in warmer weather. a new thermostat and MFTS are in the mail, but is there anything else i should be replacing which could be causing this, would rather not have to run codes and such.

UrS4boy

Your thermostat might be broken and stuck open, causing the results that you are seeing.