Badisch

We're having one heck of a sporadic behavior on our 2000 A4 that neither the dealer nor the independent shop can identify. Simply, on occasion, when you go to the turn the car off, you can just remove the key and the engine and all electronics stay on.

Replace the ignition switch you say? We've had that done 3 times now and the problem persists with no change.

More pieces of the puzzle. To turn the car off when the key is removed and everything is running, we've discovered that you can tap the brake pedal. Depress the brake pedal a bit and everything, engine and electronics, all shut off.

Less frequently, we've woken up to find all the electronics in the car on but the engine hasn't turned over. Again, tapping the brake pedal shuts everything down. Putting the key in and turning off and on has no effect while it is in this pseudo-on state.

Anybody have an idea of what could possibly connect the brake pedal to the ignition electronics? Not sure if something wrong with BSTI could cause this. The ignition switch has been replaced so many times that some plastic connectors around the steering wheel have worn out and the steering column crunches when turning now. Unfortunately we can't reproduce it on demand which makes it hard for the dealer/repair place to diagnose. Car is stock with no mods.

Any one go through this before or have some suggestions?

Thanks!
2000 A4 2.8 Avant, Tip, Xenon

Pete@ECSTuning

How are the grounds on the car? Or possibly, to high amperage fuses installed? I've also seem some interesting behavior like this in cars with water logged brake lights. It causes odd shorts - I'd start with grounds.

turbo510

It would seem that the brake light circuit, which is always hot, is getting connected to the ignition circuit downstream of the ignition switch. I'll bet that when this happens you could disconnect the ignition switch connector and still have the dash lights on. When this happens again, pull the brake light fuse and see if the lights go off, to confirm that this circuit is where the power is coming from. Are there any aftermarket alarms, stereos, etc that could be wired in wrong? Does your 2000 have any brake light warning modules that could go bad, and feed power into the ignition circuit?

SilverUrS4

Have the same issue on my 2000 A4 1.8T. Several times I have shut the car off and the engine will stay running and the dash lights will stay on but dimmer than normal. I have also come out to my car in the morning to find the battery dead several times. Battery is fine and charging system is fine. I assume that at some point in the night the ignition with go on and drain the battery.

MikekiM@PureMS

Sounds like a bad power relay.

Badisch

Apologies on the late update! From doing some further online research into the brake/transmission system's components, I had the shop look at the shift interlock.

The shop decided that, as turbo510 suggested (great call!), that brake light switch needed replacing. Knock on wood, it's now been 3 months and we haven't seen the behavior again. It had gone some long stretches without appearing before but it was getting very frequent this summer. ~$50 to replace and 2 years to diagnose.

Turbo510, no add-ons are on the car, it completely BTO stock. The car is driven Boston area city commuting every day so the wear and tear on that system isn't light.

Of course now it is in for replacing two airbag modules and the catalytic converter & O2 sensors. Not $50 repairs for sure.

~B

wwylie

I hate to dig up an old thread but it seems I cant find much on this

my 01 a4 wont shut off unless I unplug the central locking pump or pull the 20 amp fuse or the 5 amp fuse both for the central locking pump. any pointers?
I have 3 locking pumps 2 that came with the car and 1 used one that I bought and didn't make a difference

lock pumps
A,b,c
A, bad one that came with the car, with this plugged in car will shut off but locks will not operate at all

B, junkyard one that kept the car running and the locks and fobs worked

C, another junkyard one that keeps the car running. I haven't learned the fobs to this pump bc I am very frustrated with this strange little problem.

I also changed the ign switch but it made no difference.

smee3041

Thank you, for digging up those posts, I have and made a start working my way through them unfortunately the brake pedal switch fix didn't work for me as pressing the brake pedal still leaves the engine running.. I`ll continue checking out the underdash loom for shorts that is if the rain ever stops and I`ll have the diodes in the alternator checked out too and will try pulling the central locking fuses again (maybe both at the same time will prove fruitful). I suspect tracking down the source of this weird problem won`t be easy, but I`ll persevere
and will have the courtesy to post findings when I have a solution.
Still wanting to know from an auto electrical guru if an alternator power diode problem could make the ignition hot when in off position / with key withdrawn.

smee3041

Quick Update :- disconnected the leads at the rear of the alternator ....started car then switched off at the ignition unfortunately it carried on running so that's eliminated the alternator as being the culprit causing the problem.

Tried pulling the central locking fuses to no avail as car still runs when switched off at the ignition but I noticed that the boot (trunk) which previously wouldn't lock with the key was now locked. This is very strange as the central locking hasn't working since I disconnected the burnt out loom in the door. There may be a clue there more investigation is required, just need to find where the central locking module and any relays are located.

I did find this on the net and could do with an electronic circuit tester like shown here

4Driver4

Have you changed the ignition switch?