BMW 540i 1995

On older cars disconnecting the battery from ten minutes to several hours would clear the codes (and all other memory).

Not sure this works on newer cars.

I once managed to set a code to xCxx by accidentally pressing two buttons together - disconnection was the only way to clear this.

You can block starting the car from the radio? I think these BMW engineers are cuckoo if they design the car to have this feature. Are you sure the battery post is firmly seated and tightened? Does the starter turn?

Where it is all combined, you can set the code from the screen.

So what now I put in a non-bmw radio in my 540 not requiring code? Does it make the car go crazy? Or it makes BMW hopping mad?

No, not from the radio, from the OBC.

Just have your girlfriend unlock the car from the OBC using the same code she entered and then delete the code so it won't do it next time.

It's all covered in the FOM.

No not from the radio. that is the mistake, she put the some part of the radio code into the OBC instead of the radio itself and now cannot remember what part she put in which activated the start-block feature for the ignition. H