So I thought I had immobilizer problems (UK car - '96 A6 wagon) - replaced ignition barrel/key, reader coil, wiring and ignition switch, tested three keys - easier to start but symptoms remain:

I left it standing yesterday, started it 10 times at intervals no problem. But after a drive this morning for 20 mins, I switch off, it restarts then cuts out immediately (1-2 secs). NO flashing immobiliser light.

No immo or engine fault codes.

• I checked fuel pump, fuse and relay - when it works all run fine. Voltage readings appear normal
• Engine coolant temp sensor - ran all the resistance tests and 'seems' ok
• Engine multi-function sender (to guage?) - was erratic before, cleaned contacts and appears to work just fine

I'm guessing a sensor or wiring somewhere is sending a bum signal to the ECU and it's causing the shut-off. If I leave it for 10 mins after a no-start, chances are it will fire up again no trouble.

Any starters where I should look?

It's been 4 weeks now and I've spent over $100 on new lock/ignition switch - when it runs, it's a really great car. So damn annoying.

Thanks

 

I have NO idea, but a guess, and just a GUESS.....central convenience computer. I think that's the one that controls the alarm system. JUST A GUESS

 

thanks, but (I'm sure?) C4 A6s don't have that computer, but I will check the separate alarm module in any case..

 

Try swapping coil packs. It sounds like a heat soak issue, like the vapor lock of olden days. The coil pack is a good candidate for this problem.

Good luck,

Bob