Automotive vehicles are increasingly being equipped with remote starting devices. If the vehicle is within a space which is very well sealed, it is possible that the concentration of the exhaust gases may exceed desirable levels. A method and system are disclosed in which a mass-based determination of air/fuel ratio is compared with the air/fuel ratio being maintained by the exhaust gas oxygen sensor. When the air/fuel ratio based on a mass measurement deviates from the air/fuel ratio based on the exhaust gas oxygen sensor by more than a threshold difference, the remotely started vehicle is turned off.