Quote Originally Posted by GMPX View Post
Well I look at it like this, GM (or any car company) will save a dollar where they can, if the estimation routines were so good and accurate why are they fitting sensors again?
In late 2011/2012, the EPA decided that the flex fuel algorithm was not appropriate because of the following condition not setting off the correct diagnostic trouble code.

If the vehicle is running on gasoline, but has a vacuum leak, then several drive cycles will set off a DTC.

If the vehicle has the FFV algorithm, is running off E85, and has a vacuum leak, it will adjust what it thinks is the alcohol percentage to compensate (Stoichiometric AFR table references 40-70%), not setting off a DTC. That's why they went back to the sensor. Had nothing to do with the functionality of the algorithm itself.