theodp writes: Hired by the family of Brooke Melton in their wrongful-death lawsuit against GM, engineer Mark Hood was at a loss to explain why the engine in Melton's 2005 Chevy Cobalt had suddenly shut off, causing her fatal accident in 2010. Hood had photographed, X-rayed and disassembled the two-inch ignition switch, focusing on the tiny plastic and metal switch that controlled the ignition, but it wasn't until he bought a replacement for $30 from a local GM dealership that the mystery quickly unraveled. Eyeing the old and new parts, Hood quickly figured out a problem now linked to 13 deaths that GM had known about for a decade. Even though the new switch had the same identification number — 10392423 — Hood found big differences — a tiny metal plunger in the switch was longer in the replacement part, the switch's spring was more compressed, and most importantly, the force needed to turn the ignition on and off was greater. "It's satisfying to me because I'm working on behalf of the Meltons," Hood said. "It won't bring their daughter back, but if it goes toward a better understanding of the problem, it might save someone else." Next week, GM CEO Mary Barra will testify before Congress about events leading up to the wide-ranging recall of 2.6 million vehicles.