Please help - at end of tether with E46 light on dash!

For the record, this problem does tie in with me having all the BMW stereo replaced with a better one, including two Genesis amps in the boot, a sub woofer, four new speakers in doors and rear, and head unit. They also wired the Tomtom satnav power lead off the Alpine head unit rear so I don't have to plug it into the ciggy lighter.

Could it be that any of this is causing the issue?

Anything is possible but not likely that putting a new stereo and speakers would cause engine/tranny electrical problems. Did you have the fluid/filter change done?

Am I correct to say from all the posts that the problem still exists, and everyone is scratching his head not knowing what the issue is, and that the only solution is to replace this and that? Do mechanics still exists when automobiles have become so complicated the only solution is trial and error by replacing electronic boxes or reinstall software?

Nigel: I just went through a weekend of the same kind of BS you are experiencing. I did some stereo work and did not disconnect the negative cable of my battery. I turned the car back on and had that stupid transmission fault code in addition to a plethora of other issues. I disconnected the negative cable for 20 minutes and put it back on - no more warning lights and everything worked.

I know this sounds simplistic and some experts will roll their eyes at this suggestion. Your mechanics have probably disconnected the negative cable fixing other things, but why not try it again? It will not cost you anything and its worth a shot.