2010 4.6 L Tundra with 170k miles. I got the P0138 code for bad O2 sensor, Bank 1, Sensor2. Since it is the original O2 sensor I just replaced it without testing it since they are only expected to go 100-150k. Cleared the code and it came back the next day. Wiring looks good near the connector. I've read it could be that Sensor 1 is bad , that the coolant temp sensor has something to do with it, even the fuel pump relay is somehow related. Before I throw money and parts at the problem I was hoping others had succesful solutions. Thanks! By the way, where is the coolant temp sensor? Can't see it just looking around and can't find any diagram on the internet for the 4.6.