Immo (reader coil) problems - new barrel?

[CaseyJay]

Hope someone can help. I think I have immobiliser problems...

Since last week, my '96 A6 fires up every time, then stops after a few seconds. No warning lights - immo light goes out as normal.

VCDS shows up 01128 (Immobilizer coil - intermittent) and 01176 (key signal too low) faults.

Had same problem a year ago and replaced the wiring harness from reader coil to immo box. Ran fine, till now.

I suspected then that the reader is faulty so removed the barrel to check it over - it appears a sealed unit and Audi confirmed it needs to be replaced along with a new key.

Before ordering one I refitted it to check it a last time - but still no start. However I realised the immo light goes out as normal (not flashing suggesting there's a problem). So I removed the transponder and I get the flashing light - with it back in, light goes out.

Now that suggests to me the reader coil is in fact working, yet car still cuts out.

Could the reader still have some other fault? Or the bit of wiring I couldn't replace (it's hard wired into the reader, so had to splice the new one). Or are there other immobiliser problems I'm not aware of?

As for other fault codes, cannot access Engine module (have an older Hella ECU which is hard to read at times).

Really appreciate any help.

[Peter D]

You say it starts and runs for a few seconds. Is the fuel pump running during these few seconds. Place a driect feed to the output of the pump fuse and try it. Regards Peter

[CaseyJay]

sorry, only just seen this reply (thought I had alerts set up). By way of an update, the problem is intermittent - sometimes starts and runs fine. Have replaced ignition switch, reader coil, key barrel and checked wiring - but still same symptoms.

Most classic is take it for a drive, stop and it will not restart immediately. Wait 2-3 minutes and probably will.

Will take a look at the whole fuel pump system now as it seems less likely an immobiliser problem (unless it's wiring or the ecu or perhaps even old transponders - do they get weak/intermittent?)

thanks