A6 C4 (and same era Audis) Immobiliser System backup.

Posted: Fri Oct 09, 2009 9:31 pm

Another thing cracked so thought I'd share Wink

gib has been there, bought the T-Shirt, (but in fairness his car had been hacked about in the wiring dept by previous owner). He did however mention if you have the option of spares it's worth doing, and I agree, especially if you intend to keep the car for years rather than months..

Anyhow finally got the parts to try it myself, (thanks James (aka Spink ).

The immo system on our cars uses a fixed code immo transponder in the key head, which is energised and read by a coil around the ignition lock. The data is digested by the immo box behind the dash and if its happy lets you start the car.

All well and good while it's all playing nicely together, but if any of these parts gets stroppy and fails...... no starty. The key is easy you should all have a spare coded key anyway, I have one hidden on the car and in the car. (another option is to just have a spare coded transponder hidden somewhere away from the ignition reader coil)

The coil is part of the ignition lock barrel, and is just a reader, so any spare from C4 A6 should do.. or not a fortune new p/n 4A2 905 855C ignition lock with read coil

The immo box is programmed with your cars personal pin or SKC (4 digit). It can be read with Vag Tacho and the EPROM data saved to a file. This unit is mounted behind the instruments about where the rev counter is and can be sourced used some on eBay in Germany for £15 - £20 p/n 4A0 953 234 F (mine is F code, some are not, check the p/n on the box, or it will be shown in a Vag Com scan of the immo (address 25), or in Vag Tacho not sure what or if there are any differences, but logic suggests replacing like with like.

So while it's all working as it should you can use Vag Tacho to read your immo program and save the contents to file. below is my car for instance, (immo code disguised)

once pin (aka SKC) is read, you can read EPROM, when done from the file tab you can save the file..

Now disconnected Vag Tacho and turned off ignition, swapped my immo with the spare, (from a 1996 S6). I simply plugged it in didn't remove the original.

Vag Tacho was plugged in again, same procedure gives me this.

and a flashing key / immobiliser warning light and no start.

I saved the file as before, (different file name), in case I may need the info later, and then loaded the saved file from my original immo.

I clicked the "Write EPROM" button and it wrote my file to the immo. Then double checked by reading immo again, and now this immo reads the same as my original. I disconnected Vag Tacho, cycled the ignition this time no flashing key symbol and car starts.. ignition off, disconnect newly coded spare immo, reconnect to original and store the spare immo in the boot with the spare ignition lock with reader coil.

Now if any part fails it's a simple swap out to get it running again in mins, no vag com or recoding to do all you'd need is a screwdriver to get access behind the instruments for the immo box and the reader coil connector is there also in a grey foam sleeve. If the original reader coil has failed, a spare would only need to be plugged in here with a spare coded key in it to work the immo, (key doesn't need to turn the lock).

The car could now be started as normal from the original ignition lock with original or another spare, (coded or un-coded) key.

This back-up procedure can only be achieved if the original immo is working, or had been read and the EPROM data saved to a file prior to failure. I'd assume but don't know for sure that if it failed without the Vag Tacho back up data being saved you'd need to code keys and ECU to new or replacement immo box using Vag Com

Cool

Posted: Sat Oct 10, 2009 11:26 am

The Vag tacho I used was eBay sourced, and from memory was under £30 a few years ago, currently running the 2.20 version software

Camped on the site Joined: Jan 18, 2005 Posts: 325

Yet another golden gem of Info. Good job.

Just a pity about the company you keep ( Nothern pickey audi stripping lanky waster AKA Jason ( please keep calling him this)).

Bandwidth Buster Joined: Aug 12, 2006 Posts: 803

I am sure Jas11n will be over the moon you think of him in such high regard Laughing

anyway,get a decent car/haircut bought

Posted: Sun Oct 11, 2009 12:48 pm

hadn't seen you on here for a while, did you ever get to the bottom of your IQ problems?....oops perhaps I could have worded that a bit better Laughing

I Have a boost issue with mine i can't seem to solve..

I'll make a new topic about it and put a link here..

LINK

Audi Nut Joined: Apr 29, 2007 Posts: 82

Anyone have a suggestion as to Jon’s hiding places as the immobiliser is starting to play up.

Posted: Wed Sep 23, 2020 12:28 pm

Mmm. I never came across anything when I had the car. I guess you've checked inside the storage compartments either side of the boot thoroughly? Under the rear seat? Does any of the carpeted trim come off easily by the wheel arches?? If he did hide it somewhere, it'll probably be well hidden. Laughing

Incidentally I bought another A6 C4 a couple of weeks ago, so its quite possible I'll be on here in the next couple of weeks trying to sort out a few niggles! Laughing

Audi Nut Joined: Apr 29, 2007 Posts: 82

Good to hear! I hope we can help. I have another to strip for spares.

Yes been through it. I’m wondering if he had screwdriver to get to the place. Maybe behind a speaker grill in the front door. I’m thinking as he was a clever fella it wouldn’t be too far from the drivers seat.