Actually, CO2 is also a component of diesel exhaust and it can be toxic in a high enough concentration (especially if there isn't much oxygen.) I once used a pulse oximeter when wearing a mask, and while my blood oxygen level was perfectly fine, I felt like I was suffocating. I asked my doctor about it, and he said that was probably from the enriched CO2 levels of my exhalations that were being caught behind the mask and being rebreathed by me. Nothing like self-experimentation.You meant to say CO exposure I suppose, as in Carbon Monoxide?
But, yeh, normally when one thinks of being harmed by gases from fuel combustion, the real culprit is probably CO, Not CO2.