I have a 2003 Envoy SLT with 88,000 miles. The Service engine light comes on every couple od days and then goes off again. I had Autozone read the code - P0130. They say the Oxygen Sensor may be defective. Is this an easy part to replace or should I bring it to a dealership to diagnois and service? Any input is appreciated. Thanks.

This may not be an 02 issue, the pcm sees open loop conditions when the system should be in closed loop, this can be caused by other things besides the o2 sensor, a full, scan is required for a proper diagnosis.