Well last weekend I was driving around and all the sudden the light comes on. I drove it for a day then brought it to Autozone to get checked. They said the O2 Sensor in Bay 1 was slow in responding. The guy said it was the first one on the passenger side of the engine. I have not replaced it yet, and have been driving the truck around. The light suddenly went off on Monday. I am still getting crappy gas mileage though. Anyone know anything? Also what is the difference between the OBD reader at Autozone and the one the dealerships use. Because dealers are charging $80 to find out what is wrong and Autozone doesn't charge me anything. Also my brothers Jeep Grand Cherokee's light just came on yesterday so I am going to bring that up to Autozone today. Thanks for all the help.