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

Since last week, my '96 European 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 with a new key.

Before ordering one I refitted it to check it a last time - tried both keys but 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 the good key, 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). I am reading the workshop manual fault table and it simply says for 01128 - replace reader coil / eliminate open circuit.

Really appreciate any help.