I have a 2006 Honda Civic and it used to get 30/35 MPG. Now it's getting about 300 miles per tank (17 gallon tank I believe). I took it to get the oil changed a few weeks ago and that didn't change anything. I changed the air filter a few weeks ago as well and it hasn't change anything either. I took it to my mechanic and he said that no codes came up.

Other than the bad gas mileage, everything else is fine and it runs like a champ! The bad gas mileage started on our trip back from Montana (our summer vacation) to California. On the trip up we were getting great gas mileage, but on the way back we noticed that it wasn't getting great MPG. We took a trip from Los Angeles to Sacramento and that's when we realized how bad it was.


What would be causing this?

 

Things to usually do or change.. Change the Coolant, Oil, Change the SPARK plugs, Valve cover, clean the fuel injectors. and clean the throttle body,<< Make sure you idle relearn after this and careful when cleaning the throttle body if is electronic.

 

300 miles to a tank is about what i get in my 07 lx,have you check your tire pressure?

 

spark plugs i would check next... wouldn't be a bad idea to change them.

tire pressure will make a huge difference also!

 

What's the mileage on your Civic? An old O2 sensor could give you bad gas mileage without giving you a CEL.