Nearly all of Metro’s hybrid buses have a flaw with their engines that is going to take a year to fix, according to Metro. Of the agency’s 401 hybrid buses, 351 of them need repairs in what the agency officials call a “fleet defect.”

And the problem with the Cummins Inc. engines is having a ripple effect throughout the Metrobus system, causing overall bus reliability to drop. The average distance between failures for Metro’s 1,492 buses fell below the agency’s target during April for the first time this year.