You can turn off your VW Jetta's check engine light by disconnecting the battery for 10 seconds and reconnecting it, however we really don't recommend doing this unless you've fixed the problem which is causing the check engine light to turn on. Also note this process may erase radio memory and possible activate your Jetta's anti-theft system. If this occurs you will need your Jetta's security code in order to reset these systems. The safest way to turn off the check engine light is by using a scan tool.
While turning off your Volkswagen's check engine light by disconnecting the battery (or using a trouble code scan tool) you will erase the Emission Monitors as well. The smog check machine will check to see that your VW Jetta's emission monitors are complete. If two or more monitors are incomplete your Jetta will fail the smog check. So simply making sure the check engine light is turned off will not get your VW to pass the smog check. In order to "complete" the emission monitors you'll need to drive your car for at least one week in everyday driving conditions (city and freeway), in which case if the fault causing the check engine light to illuminate are not repaired, the check engine light will turn on again and the emission monitor pertaining to the emission system which is at fault will not "complete"
We recommend having a smog check repair certified smog station conduct a diagnosis of your VW Jetta's emission control computer and repair the fault causing the check engine light to turn on before obtaining a smog check.
