The smog sensor is another new feature for the 1998 Lexus LS and GS. The smog sensor is integrated into the dual climate control system works congruently with the charcoal filter and a computer to test the incoming air for pollutants. When the sensor detects pollutants, it will switch the climate control system to recirculate mode. After the pollutants are gone, the climate control reverts to its original setting. The recirculation mode is also automatically activated when the vehicle comes to a complete stop. This innovation helps to keep the interior air clean and healthy to breathe.