2004 Trailblazer with I-6 engine with 165K miles. Just bought the Trailblazer a few months ago. Getting poor gas mileage (in 2WD). I have run through tank (at different times) - 4 bottles of Techron Fuel System Cleaner, a bottle of Cata-Clean, cleaned throttle body. Spark plugs and engine air filter recently replaced. Engine runs perfectly smooth at idle and has great power.
I'm asking this because I've had first-hand experience with a different SUV. I replaced the very old OEM - O2 sensor because I was getting very poor mileage. I put in a Bosch O2 sensor and my gas mileage went up about 4 MPG.

Has anyone had first-hand experience with improving gas mileage when replacing the O2 sensor - and what brand of sensor did you use?

 

It is well known that as O2 sensors get older and accumulate mileage, they become lazy and gas mileage suffers. Hence replacing old O2 sensors with new ones is known to improve mileage. I prefer to use either Denso or ACDelco O2 sensors because aftermarket Bosch O2 sensors are known to cause driveability issues.

Another thing to try is to remove the ECM/PCM fuses for 30 - 60 minutes to allow the ECM/PCM to forget all the poor driving habits it has learned and written into it's memory. After the 30 - 60 minute time period, replace the fuses and just drive normally.

DO NOT DISCONNECT THE BATTERY - REMOVE THE APPROPRIATE FUSE(S). Why? Because when you reconnect the battery, the HVAC actuators inside of the dash are commanded to run a recalibration procedure which stresses the old brittle plastic gears inside the actuators and the brittle plastic gears break and leaves you unable to control where the air comes out, or control the temperature of the air, etc. Replacing at least one of them literally requires the removal of the entire dash! So, if you ever need to actually disconnect the battery, such as in the case of needing to install a new battery, be sure and use some kind of Keep Memory Alive (KAM) device to avoid the HVAC actuator recalibration routine.

Good Luck!

 

Thanks for your experienced advice!
So we are talking about the upstream O2 sensor CORRECT?
I've read that the downstream O2 sensor does not affect gas mileage (but just monitors the functionality of the catalytic converter) correct? So, I won't bother changing the downstream sensor because I have no codes.

 

Replace both the upstream and downstream O2 sensors. Even the downstream sensors get lazy with age and mileage! You can get both sensors from rockauto.com for about the cost of one sensor at a brick & mortar parts store.

 

What gas mileage are you seeing?

 

I replaced both the upstream and down stream sensors with Genuine GM parts (one from Rock Auto, one from Parts Geek). Gas mileage is noticeably improved. I never did check gas mileage since I usually never take the same routes, so It's difficult to get accurate measurements.