Misterious starting problems - 1995 a8 4.2

Doug773 · #1 15th October 2016, 09:24 PM

Hello guys!

I have a 4.2 V8 A8 since new.
The car has been great.

The problem started few months ago: when I unlocked the left door (it's a LH driver side car) the alarm set off, lights and horn. The car refused to start.
Then I closed the car locked again and unlocked it from the right (passenger side) door. Then I walked around and open my door, the engine started for few seconds and then quit. I did it many times with the same results.
I towed the car to my mechanic who told me the problem was the electronic door locker on the LH door, which made the car "believe" it was being robbed.
He then sent the car to a specialist on such electronic systems.
Finally I got the car back, with the advise to open the car from the right door, otherwise the alarm would set off again. Then start and operate the car normally.
I've been using the car like this, until I get the ordered left door electronic locker, which I expect for the next few weeks.
But yesterday I was unable to start the car: it was like in the beginning: the engine cranks, starts for few seconds and then quit.
Any ideas, for God sake???

Many thanks!

Doug
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HPsauce · #2 15th October 2016, 09:36 PM

Quote:

Originally Posted by Doug773

the engine cranks, starts for few seconds and then quit.

That is very typical of immobiliser issues. I'd start by getting VCDS on it and see what errors it reports.

ainarssems · #3 16th October 2016, 02:28 AM

Factory Immobilizer and alarm are not connected, you can still start and drive the car with alarm going off. So unless you have aftermarket alarm/immobilizer then it was just a coincidence that first time car did not start at the same time when you triggered alarm.

Do you have yellow warning light with key symbol on when the car does not start? If so then it's definitely immobilizer blocking engine. It is well known issue for Audi's of that era. Have a look here about fixing it http://www.audipages.com/Tech_Articl...rereplace.html

27litres · #4 16th October 2016, 06:39 AM

That Audipages link refers to the energiser coil fault.
I have come across this before and it's certainly worth checking, but based on my experience with immobiliser issues on my A4 I say also check the connection on the immobiliser box as per my instructions on your AW post...
You could also try simply unplugging and replugging the coil plug several times as well.

These intermittent faults are more likely to be connection issues than component failure IMHO.

IT · #5 16th October 2016, 10:29 AM

Quote:

Originally Posted by ainarssems

Factory Immobilizer and alarm are not connected, you can still start and drive the car with alarm going off.

I can't speak for sure on the early 1995 cars, but definitely from 1997 with the flip keys the immobiliser can, and will disable the alarm if a key is successfully authenticated.

Its documented somewhere that with the wallet key, you are able to physically unlock the drivers door, then you have 15 seconds to get the key in the ignition. The immobiliser will then disable the alarm.

At launch, you have no remote central locking, not until the infrared locking which came around 1996 iirc. So, you are reliant on a contact sensor in the door realising that you have unlocked the door, and telling the alarm that all is good. This sounds to have failed, as diagnosed by the garage, and you have a part coming.

I don't find it unbelievable that the engine start could be prevented by the alarm going off. There certainly is logic to the concept, but the important thing you said here is that is runs for a few seconds and shuts off.

As others have said, that sounds 100% like the immobiliser not allowing engine start, for whatever reason. It is usually accompanied by a warning light on the cluster though that you haven't mentioned.

VCDS would be absolutely the next best step or you're guessing blind, and im not sure where you are, but there are typically folk spread around the country who are usually happy to lend a hand in exchange for a few beer tokens

Really great to hear of a 1 owner car over that length of time btw, there aren't many can claim that

moltuae · #6 16th October 2016, 02:43 PM

Quote:

Originally Posted by IT

Really great to hear of a 1 owner car over that length of time btw, there aren't many can claim that

I was just about to say that

Wow, 21 years. And I thought I was doing well at a little over 6 years ownership of the same car, considering that some people seem to change cars more often than they change their underpants.

That's not a reference to your fleeting vehicle history of course Ian. I have no idea how often you change your underpants.

Doug773 · #7 17th October 2016, 12:39 AM

You may call it a happy marriage! Happier than my actual marriage, BTW

As for my car problem there's no lights or any other abnormal indication when I start the engine.

Thanks a lot for the cooperation guys!

ainarssems · #8 18th October 2016, 10:55 AM

Mine is 1997 S8 with flip key, here is scenario- unlock car, put key back in pocket to put some stuff in car. Get in, start looking in glovebox or setting up satnav etc and accidentally press lock button on the key in pocket. Car locks and switches on alarm after half minute or minute. Put the key in ignition , start the car, horn starts beeping as the ignition was turned on without switching off alarm. Press unlock button to switch off alarm nothing happens, a bit puzzled drive off with the horn sounding and indicators flashing. They turn off a minute or 2 later. This has happened more than once and I have since found that you need to switch ignition off first then press unlock on remote to switch off alarm.

Maybe on newer cars there is some communication over CAN between immobiliser and alarm and it would make sense that both functions work together in cars with kessy as one module handles entry and start authorisation.

IT · #9 18th October 2016, 11:11 AM

Interesting..... Never tried that specific sequence....

Perhaps the immobiliser will only disable the alarm if the drivers door is unlocked from the outside, i.e. with the wallet key, rather than generically disabling the alarm regardless of how the car was unlocked.... Easy enough to test.

Interesting thing you said though:

1) press lock button on key in pocket.
2) Car locks and switches on the alarm after half minute or a minute.

If you press the lock button on the remote, it should lock instantly, with the alarm giving you about 30 seconds before it arms fully.

If it is locking after 30 seconds, are you sure it isn't a faulty door open sensor that is missing the fact that you've entered the car after the very first remote unlock, and is simply locking the car because it thinks you never got in ?

Door open sensors are notoriously unreliable on the late PF cars....

ainarssems · #10 19th October 2016, 01:20 AM

Sorry, should have made it more clear. Car locks instantly it' s just alarm that activates 30s or so later. SometimesI do spot it and unlock car but vacuum central locking is fairly quite so sometimes I don't notice. I guess that also explains why I never missed on A6 as that locks/ unlocks with a big clonk so you always notice.

If you use valet key in door it still switches off alarm. There are contacts in the lock also on cars with remote key so that alarm will switch off when you unlock with the key in lock in case if remote battery has gone flat or when using valet key for that matter.