Are you talking about the "Check engine" light or a light that's supposed to tell you it's time for an oil change?
If you mean the CEL: Don't know where you are (geographically
For a maintenance light: Check your owners manual if you have it. There is most likely a simple "end user" procedure for resetting the light. If you don't have the owner's manual, try googling for "audi a4 service light reset". There are several results but it's not clear to me whether they are only applicable to certain years of the A4.
Hope this helps, and let us know what works for you!
EDIT: Looks like bramley computers beat me to it. This is one of the procedures listed online but one poster claimed it did not work with his/her 1998 A4 which I believe is the same generation as your 2000. Hopefully it works for you.
EDIT2: I found another possibility on wiki.answers.co
Press and hold Service button, switch on the ignition. When the service message appears on screen - press 0.0 (odometer reset). That should reset your 'service!' message.
That's worth a try if you actually have a "Service" button.
If you do need a computer to reset it, it might be dealer-only or you might be able to do it with VAG-COM if you want to buy that setup or know somebody who has one. IIRC it's some software and a OBD2<->USB cable. It's Windows only I think.
This is how to reset the light:
# Turn off the ignition
- Press and hold the button on the left side of the display while turning the ignition on
- Service OIL will be displayed
- Pull out the button on the right side of the display until the service prompt is cleared
- The display should now read ---
If the above procedure does not work, outlined below is an alternative procedure:
- With the ignition off, push the right button
- Turn the ignition on and then pull the left button
- This should clear the warning message
You can also get diagnostic readers/reset tools, or cables & software off eBay, you car should have a 16pin OBD2 port.
You need a VAG-COM cable to reset most codes on these cars as well as to do many other procedures including resetting certain convenience items such as chimes, window and lock behavior.
Ross Tech sells them as well as the software. I purchased one of the ebay knock off cables and I am using the free software from the ross tech site.
This cable is good to have if you do any of your own work. Great for checking codes and in many cases you have to have it to complete procedures (throttle body adaptation, transmission fluid checking).
Reset service light indicator Audi A4. That it is the full procedure how to reset service light indicator Audi A4. If you like to reset any maintenance oil light after an oil change. Or reset check engine light, airbag light, inspection key or insp errors when maint reqd, for Audi cars. Or any error which appears on the display. Write in the search box the car name for which you want to find information, and find how to reset other service reminders when by yourself.