The only way for carbon monoxide to be present is if you have an exhaust leak. If you never have an exhaust leak, then you'll never have carbon monoxide. Everyone please note that an exhaust leak IS very serious. My uncle fell asleap in his car with the engine running and a leaky exhaust... needless to say he never awakened.

However, the vent (there is only one and it's on the passenger side)is a GENERAL VENTILATION DUCT... it's not there for the purpose of carbon monoxide removal. If you did have the chemical present, the vent would do no good... you'd still be poisoned. Also, there are no vents on our car designed to bring fresh air in and out of the car. There is a convenience vent built into the center vents with a switch, though.

Blocking off this vent is not dangerous and will not save you in the case of an exhaust leak. Feel comfortable leaving your windows up.

If you have any concerns or would like to see a diagram of the vent, refer to the Chassis and Body Factory Service Manual.