1998 XJ 4.0L 02 Sensor question

[Jbaker]

Hi I put my jeep on a code reader and it says (02 Heater Circuit Sensor) I was just curious as to which 02 sensor that would be?? Before I go buying and replacing the wrong one... I'm getting very poor gas mileage.. I'm only running 31/10.50s and I'm getting like 9MPG which is sad considering my brother in law has the same jeep except his has an 8 inch lift with 35s and he gets like 14mpg and we both drive about the same.. He's a little more wide open then me.. But please help.. And if you could help with other stuff causing vet bad mpg lemme know!
Thanks!
-Jared

[Mudderoy]

Hi I put my jeep on a code reader and it says (02 Heater Circuit Sensor) I was just curious as to which 02 sensor that would be?? Before I go buying and replacing the wrong one... I'm getting very poor gas mileage.. I'm only running 31/10.50s and I'm getting like 9MPG which is sad considering my brother in law has the same jeep except his has an 8 inch lift with 35s and he gets like 14mpg and we both drive about the same.. He's a little more wide open then me.. But please help.. And if you could help with other stuff causing vet bad mpg lemme know!
Thanks!
-Jared

The O2 sensor closest to your engine has more to do with mpg than the other. Hows the cable?

[Carves]

Whats the actual code that you got ?

You could have a heater circuit fault because the,

... fuse is dodgy,
... wiring is shorted ... to either sensor,
... either of the two sensors are faulty.

[prerunner1982]

Jared,

Welcome to XJTalk. As Tony said the one closest to the engine, commonly referred to as Sensor 1 has more impact on the fuel metering. Sensor 2, further down in the exhaust system after the catalytic converter is an emissions sensor.

Better MPGs: Done a tune up recently? How about air filter? What was the MPG before the bad O2 sensor?