GM: 230 mpg estimate incorrect for Volt

GM's Chevy Volt

July 15, 2010 2:18:16 PM PDT
General Motors re-estimated its mileage economy for the Chevy Volt electric car.

GM says its original estimate that the volt will get 230 miles-per-gallon is incorrect.

The automaker says it was calculated using a government formula that never got final approval.

Work is underway on a new formula for estimating the mpg equivalent index for plug-in electric cars.

The Chevy Volt goes on sale in November.