Immobiliser/Starting Problem

[alan2721]

Hi

Have had ongoing problem with 1996 Audi A4 B5 immobiliser and engine cuts out after about 2 seconds. Currently overcoming this by disconnect / reconnect battery earth lead which extinguishes immobiliser light and allows me to start. After switching ignition off and back on fault reappears and battery dis/reconnect is needed to start again.

Thinking key reader coil on ignition barrel is the probable cause but why does it allow me to start every first time after the battery disconnect?

Any info to help me understand and solve problem will be gratefully received.

Thanks
Al

[bristlenose]

hi Al.
I dont want to dissapoint but i`ve had this problem for many years now.
Been back to my local vag service deptmt.only to be told,"we dont know what it is but if you spend lots of cash we will try to fix it for you".
Now after nummerous key codes and a £300-00 ignition barrel coil i still have my little car and key light flashing now and again.
Next thing to try is very exspensive so i`m told at vw.
Bring it on,someone has to get rich.

[alan2721]

Thanks for the reply Bristlenose.

Just put the car back together after airbag and steering wheel removal to change ignition switch as return spring was kaput. Whilst there I checked electrical resistance of key reader coil and wire in situ from pins 4 and 5 of white immobiliser switch box under dash - got 21ohms (20 to 25 ohms I believe is good).

Reconnected battery 1st start good but 2nd start and immobiliser light flashing (and buzzing? from engine bay which goes away after approx 10secs) engine cranks but shuts down after 1-2 seconds. So same as before really.

What else switches the immobiliser on?? Can the starter motor cause it by drawing too much current?? Why does it start OK after dis/reconnect of battery??

Thanks
Al

[kite]

I believe the chips in the key can fail............

[alan2721]

Thanks Kite,

If it was the chip (transponder) I would have thought that it would'nt start on the 1st attempt either??

Al

[wiliferus]

https://www.vwaudiforum.co.uk/forum/s...d.php?t=108709

I posted a similar thread with identical symptoms not that long ago. Problem still not cured

I shall watch here...but shan't hold my breath. Sounds like a lost cause TBH!

[aliw]

Have you tried a booster pack or jump start? Sounds daft, but I had the same with mine the other day and had to call out the RAC. They fiddled for ages and although the car was turning over with plenty of oompf, firing and then dying after about 2 sec the guy measured the voltage on the battery and it was just 12v, he put a booster pack on and the immobiliser light went out and it started straight away. Maybe a degrading battery will cause this.
Spoke to a mate of mine who works picking up salvage cars and said they have this quite regularly...turning over fine, but will not fire...put the booster on and away to go.
Might be worth a try to see if it has an effect.

[alan2721]

Wiliferus - Sorry to hear you are one of the thousands having the same problem. Not just with A4's but anything that uses similar VW/Audi immobiliser systems including Audi, VW, Skoda, Porsche etc etc etc.

I'm thinkiing there is more to the the system than the key transponder, reader coil, immobiliser box, and ECU. Obviously any wires with high resistance and faulty earths are possible.

Due to a 10-15 second buzz I'm getting from the engine bay I'm gonna look at the MAF sensor and the throttle body actuator. Anyone got any positive or negative thoughts on how these could/could not affect the immobiliser? Feel free to join the discussion and help a lot of people out - its getting too near Xmas to be spending time and money under the bonnet freezing nuts off.

I would'nt go snipping any wires attempting to disable your immobiliser as you mention in your thread. I read (on the web so it must be true lol) that with the VAGCOM the ECU can be reprogrammed to bypass it. Obviously there are problems with this and not all garages/technicians would do it. Your insurance company would'nt pay up if it was nicked - course they'd have to find out first.

Al

[alan2721]

Aliw-Thanks for your reply and I've read a lot about that problem on the web. I have'nt tried it (may do this week) but my battery reads 12.4volts and fires first time after reconnecting battery so I'm doubting that is the problem.

In fact I'll try it tomorrow and let you know.

Cheers
Al

[alan2721]

Immobiliser Fixed!

A friend at work interrogated the ECU and found a numer of error codes. He reset the immobiliser reading and the problem has not recurred for several days now. Great news and it only cost me 12 bottles of beer.

Now it has failed the MOT on a track rod end and the dreaded exhaust emissions but thats for another thread.

Thanks for all your comments and suggestions.

Al