what would cause bad gas millage
 

for the past couple weeks i have been monitoring gasmillage and it seems to be getting worse. Now a few days ago my check engine light came on and it went back off a couple hours later. I checked the codes when i got home and there were 3 of them...they were p0134, p0154 and p0300. They meant no reading from oxygen sensors 1&2 and also random/multiple cylinder missfire...i dont know if these are old codes or if they are new. Could these be the problem of my decreasing gas millage?

RE: what would cause bad gas millage
 

Erase them and if they show up again, there you go [&o]

RE: what would cause bad gas millage
 

CTS, replace it.

RE: what would cause bad gas millage
 

Could they be related to gas milage. Yes. These engines are among many that have a "limp home" mode. If they computer detects something wong, like you O2 sensor and / or the cylinders misfiring, then it enters a lower performance mode that will hopefully get the car to your house or a dealer. In this mode it is likely that gas mileage will decrease.

RE: what would cause bad gas millage
 

Is your temp gauge reading the way it always has or is it low?