Don’t catalytic converters make even ICE cars take forever for this now too? Well, depending on how sealed the garage is
Cats convert CO to CO2, and NOx to N2 (mostly irrelevant for this conversation). In closed space, the exhaust is still deadly, but you are correct in that CO would cause quicker death than CO2 displacing the oxygen.
Relatively low concentrations of CO will cause severe drops in red blood cell’s ability to transport oxygen, then follows unconsciousness and death. CO2 in contrast would require higher concentrations to be effective, as it would only reduce the efficiency of gas transfer in the lungs and lead to slow and painful decreasing blood pH - and a strong panic reflex and the ‘I can’t breathe’ feeling - until eventual unconsciousness and death.
Ah okay, my understanding is that the new way is it literally needs to replace the oxygen in the garage with exhaust fumes so you suffocate instead of the nice “going to sleep” that CO caused. I didn’t know the science behind it though.
CO2 poisoning is very unpleasant while CO poisoning is unnoticed, as is oxygen depletion. That uncomfortable feeling you get when you hold your breath is due to the buildup of CO2, breathing in an atmosphere with too much CO2 for your body to get rid of what you’re producing would feel the same.