To be eligible for a specific subsidy, the gas engine had to have less range than the better. So they electronically set the amount of gas you were allowed to use from the gas tank even though it held more. Sure the difference was only a half gallon or so but it's stealing your gasoline, and making it staler.

It was either 1.9 or 2.4 gallons depending on the model year, but they physically had the same gas tank.