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?

 

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

 

CTS, replace it.

 

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.

 

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