The 2001 Volkswagen Jetta uses OBDII (onboard diagnostics) to communicate with the car's ECM, or electronic control module. When the OBDII diagnoses an issue with the engine, the ECM flashes the "Check engine" light in the gauge cluster. Even if you know what the issue is and you replace the part, it will take upwards of 50 to 100 miles before the OBDII clears the code and turns off the light on its own. You can quickly reset the "Check engine" light on your 2001 Jetta with an inexpensive OBDII code reader you can purchase from an automotive parts supplier.
Plug the OBDII code reader into the OBDII port under the dash on the driver's side of the Volkswagen Jetta.
Turn the Jetta's ignition key to the auxiliary position, which is one click clockwise. The dash lights will turn on. This indicates the ECM and OBDII are now on. You will also see the display screen on your OBDII code reader turn on.
Select "Clear codes" on your OBDII code reader. Wait until the screen tells you the codes are clear and the "Check engine" light turns off on the dash.
Turn the Jetta's ignition key to the off position and unplug the OBDII code reader.
