Hiya people. I have a 2003 Pontiac Montana and I need to find the O2 sensors to replace them. Anyone got an idea as to where they are, or a schematic they can thorw at me? The place I normally go to wants 65 bucks to diagnose the issue, but according to my research its the O2 sensors in the van that are keeping my service engine light on. The vehicle has 93,000 miles currently.