Sometimes my parking guidance works, sometimes it doesn't and I get the message "Parking Guidance Inoperative". This can work/not work several times in one journey. Car is a 2009 CL500 (C216/2 door S class). I gather it has sensors hidden in the bumpers, when they work it will show me amber and red bars on the dash to show how close I am to something on each side, going forward or reversing.

On checking the manual there seem to be 3 types of parking aids -
1) 'Parktronic' which is standard equipment and uses ultrasonic sensors visible in the bumpers, 6 in the front
2) 'Park Asssist' which is an optional extra and uses 4 radar sensors in the front and 2 in the rear bumpers;
3) 'Parking Guidance' which is an optional extra which is radar based and scans the sides looking for parking spaces long enough for a C216. It then displays a birds eye map view and guides you into the space.
Annoyingly all three systems have the identical on/off button.

However my cars VIN list has:
230 PARKING GUIDANCE (and no other menion of 'parking').
So I assume it has the full monty, option 3. However I've never seen it working with the map view even when the distance warnings are working.

So my question is how can I check I really have option 3 and what diagnosis can I do just to keep the distance warnings showing at least?

I should add the Distronic+ cruise control is working perfectly all the time.