The "Service Engine" light appears on the dash of a Volkswagen when the computer generates and stores a trouble code, indicating a problem with the engine. Once the problem has been addressed, the best way to clear the code is with a scanning device. If you don't have a scan tool, visit an auto parts store, such as Auto Zone or Advance Auto, to have the codes cleared free of charge; as an alternative, use the generic method outlined below.
Locate the Assembly Line Diagnostic Link (ALDL) or diagnostic port in your Volkswagen: It's a small electrical device with 12 or 16 ports, usually located either in the dash, underneath the steering column, or behind the trim panels. It may have a plastic cover, depending on the model of your Volkswagen.
Connect an OBD l or ll scan device to the ALDL. Turn the ignition "On," but do not start the engine.
Enter information into the scanner as it is requested, such as the make, model and year of the vehicle. Select the option to "pull" the codes, then the option to "reset" them.
Disconnect the battery for a few minutes, starting with the positive cable, then the negative cable. Reconnect, this time starting with the negative cable. The codes should clear, though this method also resets other electrical systems, such as the clock and radio settings.
Allow the codes to clear. The service light turns itself off after the engine has been through several successful runs. If the light fails to clear, the underlying problem may not have been repaired.
Crank the engine. Drive forward a few feet, then drive backward a few feet. Do this three times, then turn the engine off. Upon cranking the engine again, the "Service Engine" light should have gone out.
If the "Service Engine" light doesn't clear, or if it clears and comes back, the root of the problem may not have been addressed, or your vehicle may have a short in the service light. A loose gas cap or an overfilled gas tank can trigger a "Service Engine" light.
The at-home tips will work for some cars, but not for others. Clearing the codes with a scan tool is the best and most effective method.