I have a 2002 A4 1.8T, 5 speed. I brought it to a garage about a month ago to have some work done while it was there the flex pipe was replaced and new coolant temp clips were installed, and new tires. Shortly after that I noticed it was running a little cooler than usual. Now it is running much colder and today the engine light came on. My garage is closed till Monday for the holiday and I am wondering what it could be and how concerned I should be. I seems to be running fine, maybe a little sluggish but that could be my imagination.

 

It's possible your thermostat is stuck open if it seems like it's taking a while to heat up.