Germany to take a second look at dozens of cars with high CO2 output

KBA will be investigating these vehicles further, not because it's proof positive of a defeat device, but because too many pollutants are bad, no matter the reason for their origin. Carbon dioxide is one of the most ubiquitous greenhouse gases, and while it may not have an adverse health effect like nitrogen oxides do, CO2 is nevertheless not great for the environment in copious quantities.

While it's unlikely that an overt defeat device, which senses a lab-testing environment and adjusts pollution control to suit, will be found, post-Volkswagen testing has uncovered some interesting things.

Many diesel vehicles tested have been found to adjust emissions-control settings based on a variety of factors, including altitude and ambient temperature. In most cases, automakers allege these systems are built to adjust themselves in order to prevent engine damage.