06 2.0 ltr Golf. Intermittant cooling system error kept turning on the check engine light. After a couple scans and resets decided to fix it. After a couple hours searching found and old thread about the same problem. To help the next guy.
Not sure what was the cause. After searching through a bunch of threads decided it was either a bad temp sensor or a bad thermostat. Rather than continue chasing the problem (its an hour drive to her house) I just changed them both, its not that expensive. Problem went away. Accessing the lower thermostat cover without removing the alternator was a PITA with a 3/8" socket and standard U-joint. If you have to do this recommend you invest in a 1/4" drive U joint and several long extensions or get a 3/8" one piece 10mm ujointed socket.