Caveat: I’m a humanities major, not a scientist, mechanic, or engineer. Still, here is my take:
Did some surfing. The website www.carbonmonoxidekills.com contains some fairly recent (2005ish) links to news stories about carbon monoxide deaths from vehicles, so it apparently can still happen. The EPA states vehicles emit about 90% less carbon monoxide than they did before catalytic converters were installed, but that still leaves 10%. And it doesn’t take much CO to kill you, since the stuff binds to your hemoglobin (the stuff in your red blood cells that carries oxygen) MUCH more readily than oxygen. As a consequence, rather quickly, your blood becomes unable to carry oxygen to other parts of your body, such as your brain. So, you fall asleep. Forever.
Scrabbler