The oxygen sensors or O2 sensors in the 2003 Chevrolet TrailBlazer are found upstream and downstream of the exhaust system. The oxygen sensor in Your vehicle estimates oxygen levels in the fumes gases leaving the motor. The oxygen sensor ought to be supplanted each 60，000 to 90，000 miles. This sensor is a wear thing and flops over the long haul. Assuming You overlook the indications of an O2 sensor issue,Your exhaust system is possible in danger and might actually make further harm Your vehicle on the off chance that it stops on You. Carbon develops and residue cakes up on these sensors over the long run. The debilitates result might pass oil,oil,or other fluid through stream adheres to the sensors.