Originally Posted by Qsilver7

I'm inclined to think that there may be an issue with your aftermarket radio installation. As mentioned already...the MID or Nav display (not sure how your e53 was originally optioned)...but the MID or Nav is the control display for the OBC...and the OBC has an additional anti-theft feature that allows you to enter up to a 4 digit CODE between 0000-9999 that can prevent starting of the car by anyone that has access to a working key.

Since that component has been removed...you have no way to counteract the implementation of this starter/ignition lockout. Since you can't see steps #4 and #5 because it requires the Nav screen or the MID...perhpas if you use the timer on your cell phone or watch etc...you might be able to start the car following the procedures below. Make sure step #1 is followed and you at least keep power disconnected for 5 minutes...ignition position 1 is a MUST DO (ign position 2 will cause failure)...then you'll need to wait at least 10 minutes for the countdown to complete...then attempt a restart: