Turbo Curiosity May 22, 2012, 04:03:35 PM The 84 EVTM shows the overboost light has a dual function.Beside being turned on by the turbo pressure switch, it is also turned on by the "direct mileage sensor".From the How it works write-up:The Direct Mileage Sensor turns on at approximately 30,000 miles and turns on the Overboost Warning/ Check Oxygen Sensor Indicator, indicating the oxygen sensor is to be checked.The component location list doesn't show a location for the Mileage Sensor.The 84 Owners Guide doesn't mention a Check Oxygen Sensor light.It disappears from the 85 EVTM. Quote Selected