The "service engine soon" light in an Audi is preset to illuminate when oil changes are due. This light is not to be confused with the "check engine" light, which indicates a malfunction in the engine management system. The "service engine soon" light can be reset when the service has been completed. Once reset, the light will once again illuminate when the appropriate mileage has been reached. All models are reset through a procedure used with the tripometer, with one small deviation in certain Audi models.
Look at the dash instrument cluster and notice the square digital odometer in the centre of the dash. There are two buttons, one on each side of the tripometer. The one on the right has a picture of a wrench on it and the other side sets the tripometer. This procedure works on Audi A4, S4, B6 and B7 models from 2002 to present.
Hold the wrench button down and turn the ignition key to the "On" position, without starting the engine.
Push the left "0" button and hold it until the message centre states "Service! Indicator Reset Procedure/ Service Indicator Reset Complete." Release the buttons and turn the key to the "Off" position.