Engine light - Emissions workshop warning

I have a 2006 Jetta TDI that has been running excellent. The engine light (along with an "emissions workshop" warning) appeared on the display as I was driving into work this week. I have 35,000 miles on the odometer. Any ideas? I'm thinking it may be a faulty sensor...any other thoughts?

I had the same thing pop up. When I vagged it, it gave me a glowplug in cyl. 2. A couple days before it was supposed to go in, the light went off so I cancelled the appt. I need to get around to vagging it again.

Get the code...it'll tell you a lot more than trying to guess