Chevrolet Captiva mirror led replacement - Chevrolet Cars & Trucks

SOURCE: Chevrolet captiva 2.0 lt poor mpg captiva has

I also have a Chevy Captiva 2L Diesel but with the auto box. The MPG on that one is abysmally bad! I bought it a few weeks ago with just under 30K miles on the clock (2007 model), and it returns around 230 miles on a full tank! That's around 17 MPG and probably on par with a Hummer!!
I was expecting the auto box to be less efficient than the manual of course but not to consume twice as much. Anyone out there with any ideas as to why this could be? I was actually already checking under the car to see if it loses fuel... We live in the suburbs and our trips can be considered a mix of urban and extra urban (they are admittedly on the short side and from a cold winter start; still, this doesn't justify the extremely low MPG). The car seems adequately powered for its weight and considering the small'ish engine and auto box.
Thanks!