2001 GMC Sierra 2500 Q&A

2001 GMC Sierra 2500 Question: O2 Sensor and poor MPG's

I have a 2001 GMC 1500 4.8l and I am getting 11-12 mpg's on the highway, could this be an 02 sensor? My air filter is new, plugs, wires, and fuel filter are also new. -
Answer 1
If you had an oxygen sensor causing that much of a fuel economy loss, your OBDII check engine light would come on based on a "lean" fuel trim issue. A good diagnostic test is in order to see what is going on with your truck. A solid fuel economy test should be done. Make sure there is nothing causing an issue aerodynamically. -
Comment 1
There is a check engine light on, I will shoot up to Autozone and have them check the code. Thanks Dave! -
Comment 2
OK, yes, check the check engine light - and if you have P0171 and P0174 together, you have a vacuum leak, air intake leak or something like that...which will make the engine ask for more fuel. -
Comment 3
I checked the code today, it said engine cylinder misfire... -
Comment 4
This too can consume more fuel, if fuel is unburned by a misfiring cylinder. Or, worse yet, you could have a fuel injector on the misfiring cylinder sticking open. Check your oil level - does it smell like fuel at all? Is it high at all? These are just thoughts. A good diagnosis is in order, otherwise it will be lots of guesswork. Good luck. -
Comment 5
Thanks Dave, I will have too look into it a bit deeper. -