MINI is recalling 30,456 Cooper and Cooper S cars in the U.S. to address poor side impact protection. This includes 15,653 examples of the 2014-2015 MINI Cooper Hardtop, 14,782 units of the 2014-2015 Mini Cooper S Hardtop, and 21 of the 2015 Mini John Cooper Works Hardtop. Those with production dates between December 2013 and March 2015 are affected. An additional 4,130 MINI hatchbacks are being recalled in Canada.

The issue was discovered during a recent NHTSA-conducted side impact crash test, according to documents posted on NHTSA’s website. According to NHTSA, the agency tested a 2015 Cooper and Cooper S Hardtop on July 1 and 2, but the S didn’t meet one of the impact requirements.

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In affected vehicles, rear-seat passengers could be at a higher risk of injury after a severe side impact, NHTSA said. To remedy this issue, additional energy absorption material will be installed between the rear interior side panels and the body of the vehicle. BMW is not aware of any injuries linked to this issue.

The campaign to fix them will begin on Sept. 12.