What might cause my 2005 Volkswagen Beetle check engine light to come on?

There are a huge number of reasons the check engine light might come on in any vehicle, let alone Your 2005 Volkswagen Beetle. It's essentially a catch-all light that indicates that You need to scan Your vehicle with an OBD2 tool to get more diagnostic information. The causes are numerous and widespread, but I'll do my best to cover some common scenarios. On the '05 Beetle in particular, the most common issues are an EVAP system fault, a bad O2 sensor, a plugged catalytic converter, a defective airflow sensor, worn spark plugs, or a bad thermostat. These range in severity, and they're only a small subsection of what can go wrong. If You don't have personal access to an OBD2, take Your Beetle to an automotive parts store -- places like Advanced Auto Parts or Autozone will scan it for free.