2001 Code P1131

Passenger side O2 sensor. First one up near the header pipe. You can't miss it. It's the most difficult sensor to access. Sensor is most likely faulty, and is also the cause of your poor gas mileage. Sensor is thinking there is not much fuel being burnt on passenger side, it detects lean (in a fault) so it over compensates by adding more fuel to the mixture on the passenger side injectors. Therefore decreasing your fuel mileage. You can replace yourself, but it's difficult to get to to. I had to end up breaking the end of my sensor off so I could slip a socket on the sensor base and un thread it. it's a pain in the a$$, primarily because that specific sensor is so close to the firewall that it's so hard to get a socket onto it, let alone the special O2 socket. You can do it, just the sensor is about $50 - $60 a piece for the front ones.