Originally Posted by wpoll

You cannot test the system if it's in failure mode like this - a single failure in the system disables the entire system.

Easiest why to diagnose it is with a BMW scan tool - this will tell you exactly which sensor (or wiring path) is causing the system to go into "failed" mode.

Mine is currently like this too - in my case INPA is telling me the front left sensor sensor has failed. It comes and goes - I'm living with it while the part ships.... and I figure out a way to change the sensor without dropping the front bumper.

Yes, I know you have to drop the bumper (on a facelift) bit this ONE front sensor can be accessed from the left tow-hook hatch, using dental tools to release the catches etc. It's like key-hole surgery but I think it's possible. I've pretty-much had the old sensor out this way...