P0300 GMC -

Question

could a bad oxygen senser cause ths, or a bad connection to an oxygen sensor

Answer 1

HI there,

Normally a bad O2 sensor will not cause this. What you might get is a code for the sensor because the engine is not running properly. I would start with a tune up and checking for intake manifold vacuum leaks to resolve the misfire issue, then clear the codes and if the O2 sensor codes return,work on the sensor that is failing.