Hi everyone : " Merry Christmas and a very Happy 2011" to all car enthusiasts :) My E39/S62 is throwing up a " 91 " code ( mechanic tells me this ) which apparently is " Function Oxygen Sensor Control ".......I cannot find this number fault in my trusty Bentley workshop manual ! Can anyone please help explain to me what this fault means and what do I need to ( pay for ) do to remedy it ? It causes the engine to fail to rev beyond about 3500rpm when it does occur but it is so intermittent I have had difficulty explaining the symptoms to my ( trusty ) mechanic ! Cheers from VERY WET North Queensland Australia ! :D