Car exhaust .....
The combustion products produced by a car engine contain a variety of chemicals due to the partial oxidation of the fuel. Only the complete combustion of a hydrocarbon produces only CO2 and water vapor. That is never the case in a car engine. The O2 is limited. Therefore, there will be a mixture of products: CO2, CO, C (soot), plus the "pieces" of larger hydrocarbon molecules.
This is where another important part of the exhaust system comes into play: the catalytic converter. The catalytic converter further oxidizes CO to form CO2, and oxidizes those "pieces" of larger molecules into CO2 and water vapor. The catalytic converter also converts NO (NOx) to N2.
Interestingly, it is almost impossible to commit suicide with a modern car by running it in the garage, since so little carbon monoxide is produced. It's possible that the would-be suicide committer will simply get bored waiting for something to happen, reevaluate the situation and shut the car off. I'm not making light of suicide attempts, but I am saying that the use of catalytic converters has made using car exhausts more difficult as a means to that end.
The bottom line is that the gas emitted at the tailpipe of a modern car consists primarily of CO2, N2 and water vapor, with very little CO or other hydrocarbons, or NOx.