Hello - I just bought a 2004 Jetta - day one - mil light came on. Car runs fine. What could it be? 2 mechanics checked the car over before I bought it and carfax said it was one owner no problems.

Hello Zach. my name is Andy and to start with the best way is to connect the obd2 scan tool into it that way we can gomore straight to where the problem is and avoiding dealer fees or mechanic fees which they are really expensive and avoiding replace parts unneccessary

First off, let's simply define the OBD-II Trouble Codes:
Yes, 18032/P1624/005668 are the three codes that indicate "MIL Request Signal Active."
So, what does THAT mean (in plain English)??? This means that Fault Codes are stored in the TCM. SO WHAT'S THE SOLUTION?
MyAirbags has a reset solution for 04-07 VW Jetta 1.8L/2.0L https://www.myairbags.com/product/vw-jetta-2004-2007-1-8l2-0l-ecu-ecm-pcm-repair/ as well as the VW Jetta 02-06 2.5L/2.8L
https://www.myairbags.com/product/vw-jetta-2002-2006-2-5l2-8l-ecu-ecm-pcm-repair/
You need to have the TCM reset to its original status. https://www.myairbags.com/how-it-works/ecu-ecm-pcm-tcm-unit-repair https://www.myairbags.com/engine-control-unit-repairs-ecu-faqs

Dodge Forum stated something about have the PCM reprogrammed may be in order after replacing/getting this code....said there was a tsb for it..NUMBER: 18-015-09

did you replace stereo

TAKE CAR TO AUTO ZONE THEY WILL SCAN IT FREE AND GIVE YOU TROUBLE CODE.

Your going to have to get your car scanned for the DTC codes. The Cars ECM has detected an issue by setting the MIL light to come on, It could be as simple as a faulty gas cap to a faulty O2 sensor, Good luck and Auto Zone scan free of charge.

could be several problems, you need to have a diagnostic check done to determine the fault codes, then have them interpreted

Probably a bad COIL-PACK

might be a plugged catalytic converter or the O2 sensor. cheap gas.

sounds like a coil pack failure,get it code read,your mil is flashing because its a cat damaging misfire !!