Wrong. I owned the 5D Mark II for a long time and Auto ISO certainly goes well beyond 400. Can we talk you through this? Switch to Av mode and Tv mode, auto ISO and go in a darker room and meter. In Tv mode set aperture to like f/8 and shutter speed to 1/500, something where you need a lot of light. The ISO should go well, well above 400 after metering. Now switch to M mode and see what happens. In M mode I always set my ISO, so cannot recall whether in M mode ISO can be set to AUTO like in the 1D series. Make sure there are not advanced settings somewhere set. I did that on my 1Ds3, had a setting deep in a menu set whereby I couldn't autofocus. When I finally found after having contemplated crashing camera out upstairs window, it worked fine.