At the heart of the G.M. recall of 2.6 million Chevy Cobalts and other models was a tiny metal pin called the detent plunger, which would normally serve to hold the ignition in the “run” position.

Q. I have a 2009 Chevy Cobalt. The car was running but had some fault codes, one being a faulty ignition switch. I replaced the switch and did a key relearn, and now the car will not crank or start.

Honda Motor Co. is recalling the popular Accord and Civic passenger cars to address problems with an ignition switch that could allow the key to be removed without the transmission being shifted into ...