Mileage Calculator Wildly Inaccurate
 

I've looked everywhere and can't find where you can change the correction factor in a hidden menu to make your mileage calculator and distance to empty more accurate. My 50i gets 14-15mpg in reality but shows 23!

The 3rd and final hidden menu [hidden OBC menu] - BMW M5 Forum and M6 Forums

See test 20. I think your error is outside the adjustment range though.
I had a strange problem with MPG readings. I had just retrofitted the CIC Nav to my '08 3.0si and my keys were reading different MPG's. One was correct, the other was reading 20% higher then the first, like it was reading UK MPG. Settings in idrive were correct. I changed iDrive setting to l/100km and then back to MPG and both keys read the same.