Quote Originally Posted by rjsdavis View Post
Ok - all fuses checked and now working. Front cigarette lighter now working also... Rear tailgate light replaced and now working fine.

Still got the serious power drain - only last thought that I've got, is that the cigarette lighters remain "on" after the car has been shut down and locked. That is to say, that if you leave a mobile charger in either of them, they still continue to be powered after the shut-down and lock. Shouldn't they only come on with the ignition? It's not like they go off after a while either - they remain on, for as long as you leave something plugged in.

This isn't the actual power drain though (I.e. I'm not leaving things plugged into them) - I was just wondering aloud if this could be linked to the cause?

Short of that, I've got nothing!

Ok, so it was the Control Head all along. GGGGGGGGRRRRRRRRRRRRRR.

In the end, it was the Control Head, that finally failed as a unit, taking the whole MMI system out with it. It is now clear, now that I understand the system a little better, that the previous MMI related gremlins, were actually early indicators that the Control Head was a failing unit - leading upto the failure. These early indicators were:

1 - Loss of sound - only resolvable by an MMI system reset.
2 - Loss of MMI screen - only resolvable by an MMI system reset.
3 - Sometimes the MMI control panel lights didn't come on - only resolvable by a full engine restart
4 - Causing the car to take an awfully long time to shut-down, sometimes never shutting down, leading to a massive power drain from the battery - signs of the system not going off were the hazard light indicator on the main dash never going off, or taking a very long time to go off - which indicates when the car has actually shut down and stopped drawing power.

I sourced a replacement Control Head from a breaker on eBay (25), which I couldn't order until I had removed my one, to make sure I had an exact parts number match - there are variances.

I was able to fit the CH myself, but it was immediately clear from a VCDS scan, that Component Protection was active (which to be fair I was expecting). After a lot of searching around, with prices mostly ranging from 100-150 to remove CP, I found CT Cars in Surrey, who charged me the very fair price of 40 to do it - while I waited, with coffee - on an appointment basis. They were brilliant, very fair and went about their business without any fuss or problem. Big shout out to those guys!

This was actually completed about two months ago now, but I've been running the car to make sure all was well before I shared it. I've had zero problems with it. The MMI has given me no jip whatsoever, so the CP removal was permanent. I've had no further power drain issues at all - and the CH is the only part that has been changed in the car's entire system. I now have a completely clear VCDS scan, which is totally awesome as I haven't had one of those in a long old time!

Many thanks for all of the posts and replies that have helped me to slowly work out what was wrong with my car. Even the electrical specialists in Sandwich weren't even able to close to diagnosing it - and simply wanted to replace individual components until they eventually found the culprit.