Turning ignition on for 30 seconds ( or thereabouts ) without starting the engine works - this isnt in the Bentley manual, I got the info from an anonymoous poster to their tech news goup. As to resetting after a while, I cant tell, if you class a couple of weeks ( thats about
250 miles for me ) as a while, then it didnt work on my 1999 E46, but it does work on other cars, I believe.Steve