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.
How the Detent Plunger Works Pin Plunger Basic Switch
When the ignition key is turned, it rotates a plastic disc inside the ignition switch. A small metal part, called the detent plunger, slides into notches, or “detents,” in the plastic disc. This is what should hold the switch in either the “run” or the “accessory” position.
Early model detent plungers were slightly too short, so the plastic disc could slip out of “run” and back into the “accessory” position, causing the car to stall.
The problem was made worse by a key that had a wide slot. A heavy key ring swaying in this slot, or jostled by a knee, could pull the key out of run, into the “accessory” position.
If the ignition were switched off while the car was in motion, as could happen in the faulty Chevy Cobalts, the main computer controlling the airbags would stop working after one or two seconds. If the car crashed after that period, then the airbags would not deploy.
How the Detent Plunger Works
When the ignition key is turned, it rotates a plastic disc inside the ignition switch. A small metal part, called the detent plunger, slides into notches, or “detents,” in the plastic disc. This is what should hold the switch in either the “run” or the “accessory” position.
Early model detent plungers were slightly too short, so the plastic disc could slip out of “run” and back into the “accessory” position, causing the car to stall.
The problem was made worse by a key that had a wide slot. A heavy key ring swaying in this slot, or jostled by a knee, could pull the key out of run, into the “accessory” position.
If the ignition were switched off while the car was in motion, as could happen in the faulty Chevy Cobalts, the main computer controlling the airbags would stop working after one or two seconds. If the car crashed after that period, then the airbags would not deploy.
How the Detent Plunger Works
When the ignition key is turned, it rotates a plastic disc inside the ignition switch. A small metal part, called the detent plunger, slides into notches, or “detents,” in the plastic disc. This is what should hold the switch in either the “run” or the “accessory” position.
Early model detent plungers were slightly too short, so the plastic disc could slip out of “run” and back into the “accessory” position, causing the car to stall.
The problem was made worse by a key that had a wide slot. A heavy key ring swaying in this slot, or jostled by a knee, could pull the key out of run, into the “accessory” position.
If the ignition were switched off while the car was in motion, as could happen in the faulty Chevy Cobalts, the main computer controlling the airbags would stop working after one or two seconds. If the car crashed after that period, then the airbags would not deploy.
Large Snap-Acting Switch Sources: McSwain Engineering; Hallman Engineering