Unique Calibration
WARNING: This page is about a different car, the 2005 Ford RV Cutaway, 2005 Ford Econoline, 2005 Ford E450 Super Duty, and 2005 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
The Emission/CAFE/CO2 Compliance Department is responsible for assigning calibration numbers. Unique calibration identifications are assigned to cover similar vehicles to differentiate tires, drive configurations, final drive ratios and other significant certification factors.
These two characters are chosen by the analyst to provide identifiable information unique to each calibration. For example, using the number 2 to denote a two-valve engine and 4 to denote a four-valve engine, provides an easily identifiable difference.