Ford Motor Co. ended its Firestone tire replacement program on March 31, which cost the auto maker $2.1 billion after taxes and was a contributing factor in its $5.4 billion loss last year.

Ford began the free program last October to replace potentially defective Firestone Wilderness AT tires on Explorer SUVs and some other Ford SUVs and pickups. Ford says it has thus far replaced 10.6 million tires out of an estimated 13 million. A spokesman for the auto maker says the 13 million figure was a broad estimation of the possible number of tires out there, and Ford feels confident it has replaced about all of them.