Hot alternator does not sound right, the other thing that rang a warning bell was you saying that the electrical system had drawn 50 amps with the accessories all switched on, that sounds too high to me but not if it included using the electric power steering.

Small update.

In the meanwhile I've replaced the alternator completely by a genuine Bosch refurbished 90A one with 50mm pulley.

The one I've taken off (which was bench checked by a shop) has a 57mm pulley but the plastic cover suggests it was 90A as well.

But at least it means it was spinning at lower revs.

 

Next to that got a tip to check the wiring underneath the battery box. Had it all opened up and cleaned, no trouble found up to / in to the bulkhead.

 

As for now it hasn't occured yet, but it's gotten colder so hope it stays away.

On 29/09/2022 at 22:27, J.R. said:

Hot alternator does not sound right, the other thing that rang a warning bell was you saying that the electrical system had drawn 50 amps with the accessories all switched on, that sounds too high to me but not if it included using the electric power steering.

50 amps was with all aux options on. Rear window heater, fan, blower, etc. Was reading in VCDS at that time the load indication was 50%. Cig plug reading was only 12.0v, haven't checked what it's showing with the new alternator.

Well, all the gremlins are back. Some single trips can be without faults, or directly giving the same behaviour after key-on. Today a new intermittent fault: parking brake signal indicating it's on disabling ABS. Went away while driving.

 

I am really wondering how this is possible, must be a central module transferring these signals.

Please note - I am not a mechanic or expert in anything.

 

Thoughts -

 

other than what you've already listed, have you fitted any new or changed parts, standard or non-standard, or added in extra items or made any conversions

 

anything thing done a bit before you started having these problems

 

any water leaks on the vehicle

 

did you check connectors sockets, plugs, pins, wires for crud or damage

 

any sort of pattern to issues - it's hot, cold, raining, after being parked up, electric load, etc.., etc..

 

That me out of ideas, other than all earths but there are so many.

   

Update. After the spring the issues started again when outside temperatures rose.

I got in contact with a German head mechanic working for VAG, after explaining my issues he immediately said: '09 chassis? We've had this before and in the end we replaced negative ground cable from chassis to battery.

 

So I followed that and replaced that though no signs or damage and hey presto issues are gone since June. Part nr: 6Q0971235H - Wiring set for battery

 

Hope this helps whoever gets into similar issues... It must be thermal and/or current load that's causing the internal resistance to rise. Static measurements do not give me indication of a fault.  Terminal ends are clean and not corroded.