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24 February 2006

A3 CAN System Long Coding Worksheet & Instructions (for use with VAG-COM)

Read the background information on this page. For a lot of common items, you may not need the spreadsheet linked below. Instead, see my VAG-COM Coding Reference. The files linked below are useful for a 'big picture' of what's going on with the Central Electronics and Comfort System coding, or for a few settings which aren't covered in my other instructions.


November 2011: UPDATE. I received this from another A3 owner and am adding it as a caution when using newer versions of VAG-COM

"I've got some information to add. It's actually kind of important, as it pertains to VAG-COM.

I met up with a guy who has a VAG-COM cable to do a code clear and also customize some programming using one of your procedures. I followed the instructions for "Enable Auto Window/Roof From Remote". The latest VAG-COM software has changed a bit, and it's more user friendly. In the Central-Conv section, Byte 03 and 04 don't have any labels but 05 does, with a number of checkboxes to set the desired behavior. I went ahead and put in the hex updates to 03 and 04, then the 05 setting. It worked. However, I discovered later that the fuel door switch was somehow disabled! There was no way I could get the door to open. Thankfully I was able to get back to the guy and refresh my system back to the original code. Then, I updated Byte 05 only this time. It worked--the fuel door was active again and the windows responded to the fob controls--disaster averted.

Anyway, I was really lucky in that I hadn't refueled prior to the VAG-COM change. I could have easily ended up several days later going to get fuel and dumbfounded by the fuel door not opening... and possibly having to bust it open. It might be worthwhile to just add a warning message to the blog that the steps outlined for programming VAG-COM are on an earlier release, and that in some cases they may not work properly with the latest release."

The A3 is part of a new generation in automotive electronics, which brings a new ability to customise it easily.

In the past, any electrical accessory had to be wired from the battery, usually through a switch, to the device. It worked however it worked, and couldn't be easily reconfigured. This meant greater complexity and expense, and difficulty adapting cars for different markets. For example: with power windows, every window motor had to be wired through it's own switch and through the set of switches for the driver (if so equipped), making for a complex wiring harness. Headlights/taillights wired up for the European market couldn't be easily converted for the US market, and vice-versa.

With modern technology, everything is different. The A3 handles everything through a central computer system. Every switch and device is a node on the Controller Area Network (CAN) which runs throughout the car. This means that many features can be modified by altering the programming of the CAN system computer.

I won't go into a lot of detail about the wiring, but here's a comparison of old vs. new:

The old way: Turn parking light switch 'on', 12v current flows through switch to the parking light bulb(s), making it light up. Step on the brake pedal, switch closes allowing 12v current to flow to another filament or bulb, making the brake light come on. The brake light is brighter than the tail light because of the difference in bulb wattages.

The new way: Turn parking light switch 'on'. Computer gets the signal from the light switch, and applies reduced voltage to one or more bulbs on each side, making them glow at 24% of their maximum brightness, to act as tail lights. Which bulbs are activated, and the percentage of brightness, are dependent on the settings in the car's computer. When you step on the brake pedal, the computer gets a signal from the brake switch and increases the tail light voltage to make the bulbs glow at 100% of their maximum brightness to act as brake lights. Again, which bulbs are affected is dependent on the computer settings. Change the settings == change the behaviour, no re-wiring needed.

There are a lot of settings which are for compliance with regulations in different countries (e.g. lighting), and others which are simply marketing choices. What is great for us is that Audi has chosen to not lock this down, so that anyone who has the proper (hardware & software) tools can modify a lot of cool stuff.

About those tools..... There are three choices:

  • The 5051 or 5052 devices which VW/Audi dealers have. These are not for consumers, and are not easy to operate.

  • VAG-COM, from Ross-Tech, with the HEX-USB+CAN Interface. This is the most common for enthusiasts, and is very full-featured. However, I think a little competition would be good for them, so I'll also mention...

  • VAD Pro (formerly known as ProDiag HD from Shade Tree Software).

I'm not going into details of how to operate any of the tools here, or debate which is better. Instead, I'm going to make it easier to change some of the settings in the A3 computer by providing a spreadsheet and some notes.

All of the settings information I originally obtained from en.openobd.org and de.openobd.org, and refined through experimentation. I thank the guys who run that site for their work, and encourage you to check it out as an additional resource. For the specific A3 long coding settings, I think my presentation is more usable and some of my descriptions are more easily understood than the German translations that you'll find elsewhere.

Some of the settings that are possible on the A3 are made through 'adaptation', which is basically using something like VAG-COM to pick various choices out of a menu. Other settings, though, are done through 'long coding' which involves setting of individual bits & bytes in the programming. I have made what I think is the best, safest, most understandable and efficient method of editing the long codings for the Central Electronics module and the Comfort System module. This is how you can enable one or both rear fog lights (if you have the correct light switch, not a standard USA-market one), enable auto-closing of windows and sunroof (and auto-opening of the windows) from the remote, change tail light & front fog light configurations, etc.

My solution is developed in a spreadsheet. It contains multiple worksheets with an explanation of 'long coding', instructions on how to use the spreadsheet, and worksheets for the Central Electronics and Comfort modules on the 2006 A3. The spreadsheet was developed in OpenOffice, which is a Free (in every sense) office software suite for Windows/Linux/Mac OS X. Links to download it are provided below. I'm also providing instructions on how to set some preferences in OpenOffice to make it work best for you. The spreadsheet file is named with the version number. With it open in OpenOffice, you can also do File --> Document Properties... to get version information.

You CAN redistribute this, as long as the copyright notices are intact. If you redistribute a modified version, you must include my original along with it (consider it the 'source code'). I do not support converting it to Excel, Lotus123, or any other proprietary format. If you do so on your own, make sure you (a) take responsibility for supporting that yourself if you redistribute it, and (b) attribute and include my original along with it.


If you are only interested in looking at some information, then here are some PDFs generated from the spreadsheet. Note that the long codes have been zeroed out, so DO NOT attempt to 'use' the PDFs to figure out your long coding solutions! Use the spreadsheet instead! These are just for reading material...

Please email me with any feedback or questions, using the "Email me" link in the upper left of this page. This article will be revised/updated as necessary, and revisions may not be noted. Please consider referring other people to this article to download the items rather than passing them on yourself, since I may have updated something since you downloaded your copy.


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