Where is the 2003 chevy trailblazer oxygen sensor located?

The oxygen sensors or O2 sensors in the 2003 Chevrolet TrailBlazer are located upstream and downstream of the catalytic converter. The oxygen sensor in Your vehicle measures oxygen levels in the exhaust gases exiting the engine. The oxygen sensor should be replaced every 60,000 to 90,000 miles. This sensor is a wear item and does fail over time. If You ignore the signs of an O2 sensor issue, Your catalytic converter is likely at risk and could potentially cause further damage to Your vehicle if it quits on You. Carbon builds up and soot cakes up on these sensors over time. The exhausts output may pass grease, oil, or other liquid through its stream that sticks to the sensors.