Audi A4 / Check Engine Light (MIL) / What it means / How To Turn it Off

A few days ago, my wife started the car and noticed the check engine lamp (also known as the malfunction indicator light or "MIL") remained illuminated. I opened the owner's manual to see if it provided any clues, and it basically said that it is part of the car's OBD II system and that I should take the car into Audi service to have them diagnose the trouble. This of course means that if I want to know what has caused that lamp to illuminate, it's going to cost me a half a shop labor hour, or approximately $55. Paying $55 dollars, plus the inconvenience of the trip to the dealer, only to be told my car's problem was something small like the gas cap not being tightened, not only seemed like a huge waste of time, but an expensive one at that.. Instead, what I did was put the money into a diagnostic tool that I can keep in the car and use to diagnose these problems myself.

OBD is an abbreviation for On Board Diagnostics and if your car was sold in the United States after 1996, the US Government has federally mandated that it have an ODB II interface (regardless of make or model). With the right diagnostic tool, the OBD II interface will allow you to retrieve a code that explains what caused the check engine light to activate, to turn off or "reset" the check engine light, and (with some of the higher end models) retrieve real-time data and potentially make other tweaks to the settings in your car's computer.

Warning

THE MALFUNCTION INDICATOR LIGHT MAY INDICATE A SERIOUS PROBLEM IN NEED OF REMEDY BY A TRAINED PROFESSIONAL. UNDERSTAND WHAT YOU ARE DOING BEFORE YOU DO IT. THE MATERIAL AND METHODS PRESENTED HEREIN ARE NO SUBSTITUTE FOR HAVING YOUR CAR CHECKED BY A TRAINED PROFESSIONAL. I AM NOT RESPONSIBLE FOR ANY DAMAGES CAUSED BY THE USE OR MISUSE OF THIS INFORMATION. PROCEED AT YOUR OWN RISK.

The first step is to locate your car's OBD II Interface, on a 2002 Audi A4 Avant Quattro this can be found on the driver's side, directly behind the hood release leaver. You will not generally be able to see it without looking under the dash.

How to Replace a Brake Light Bulb on an Audi A4 Avant Quattro 2002

Somehow I was not surprised to read in the owner's manual that I needed to take my car in to the dealer simply to change a bulb. The owner's manual blames this on the fact that cars are becoming increasingly complex (which is of course their own fault).

I called my local Audi dealer and they quoted $80 (USD) to perform the repair service. Instead I went to the auto parts store and bought a replacement bulb set which contained two (P21/5W) bulbs for $3.97 (USD).

Warning

EASY DOES IT!  WHILE STRAIGHTFORWARD, THIS PROCEDURE REQUIRES PATIENCE AND CARE. UNDERSTAND WHAT YOU ARE DOING BEFORE YOU DO IT. I AM NOT RESPONSIBLE FOR ANY DAMAGES CAUSED BY THE USE OR MISUSE OF THIS INFORMATION. PROCEED AT YOUR OWN RISK.

First I carefully opened the circular cover with a small flat head screw driver (it just pops out).

Then, using a Phillips head screw driver, I carefully loosened the screw that holds the entire light assembly in place.  I knew I had the correct screw because as it got looser I was able to move the assembly slightly.  While the screw might have been able to be recovered with a magnet if it had fallen in the body, I was careful to avoid this by only loosening it a bit at time.

Once the assembly was free of the screw, I gently pulled back the rubber material so that it was free of that rubber block.

Next I began to carefully pull the assembly away from the center of the car.  In this case (because it's the left assembly) I began by pulling it gently to the left (not directly out because of the two plugs). I did this carefully as not to damage the plugs.

Once both plugs (top and bottom) were free of the body, the assembly was only connected by the wire.

 

Next I disconnected the socket from the assembly by carefully inserting a small flat head screw driver.

 

 

Finally I carefully separated the white piece from the assembly.  The stop light bulb was the one at the bottom (it had two filaments).  To remove it, I pressed down very gently and rotated it out counter-clockwise.

 

If you can' stand the thought of paying $100 just to have someone hook up a little cable underneath your dash to clear out a light, this is for you. We've all had that conversation... "Oh wow, you fixed it already? You just needed to erase the code, huh? Wait, how much? You're kidding. I saw what you did, I was standing right here the whole time, it took 10 minutes." THAT COSTS $100?!?!?!