If you can smell it and it smells like exhaust fumes, park it and call the manufacturer, CO2 can be deadly. If it is diesel fuel prior to combustion, that is also a hazard, and while remote, can catch fire. I would tell the dealer to come and get it, and don't bring it back until it is safe to drive. If it is diesel fuel, they should be able to see where the leak is, the stuff attracts dirt so it should not be hard to miss, and they can die the fuel and use a blacklight if they think it is vaporized diesel, which is extremely flammable.