The change got the Fit an "Acceptable" rating in a second test, and earned it a "Top Safety Pick" designation.
High crash-test scores are important because they help allay buyers' concerns about whether tiny subcompacts can adequately protect a driver and passengers in a sea of larger vehicles. Of all subcompacts, only the Fit and the Chevrolet Spark won the "Top Safety Pick" designation, the institute's second-highest rating.
Honda Motor Co. started installing the stronger bumpers at the Mexican factory that builds the Fit in June. a rare step for an auto company, Honda is asking owners of all 12,000 2015 Fits sold before then in North America to return them to dealers, who will replace the bumpers.
"We want to make our cars as safe as we can make them for our customers," said chief safety engineer Chuck Thomas.
The replacement should take about 30 minutes, Thomas said, and involves removing the original bumper beam and bolting on the stronger one. He couldn't estimate the cost to Honda.
IIHS crash test results are followed widely on the Internet and are especially important for subcompacts, which by design have less structure to absorb the impact of a crash, said Karl Brauer, senior auto analyst at Kelley Blue Book. Subcompact sales are down just under 1 percent so far this year, and the poor crash test scores for most of the segment are partly to blame, Brauer said.
Many buyers, he said, wouldn't consider a subcompact it didn't get at least an "Acceptable" rating on the overlap test or a "Top Safety Pick" designation. "Just having not failed would make some people open to considering the car," Brauer said.
Honda sold nearly 27,000 Fits through July, down almost 12 percent from a year ago. The Chevrolet Sonic is the top-seller in the segment, at almost 57,000, according to Autodata Corp.
Russ Rader, an IIHS spokesman, said it's rare for automakers to call cars back to dealers after they are retested, but it has happened about two dozen times since 1999. Most were to change air bag deployment or fix post-crash fuel leaks, he said.
All Fits built on or after June 9 have the new bumpers. Honda will notify owners of Fits without the stronger parts starting in late September and replace the beams free of charge.