Fuel consumption.

Is this city, highway, or mixed driving?

Are you experiencing winter-like weather in your area?

How are the tire pressures? Are they the correct size?

I think EPA's highway rating for this version of Corolla is 39 miles per U.S. gallon on the highway; my folks have managed to get 40mpg on a few occasions with their '04.

Hey High Tech,

Yes I was talking about Imperial gallons, so it works out about

I think the OP's car is a diesel, not currently sold in the U.S.

There must be something wrong. My Panda diesel never does less than 60mpg and I would expect your D4D to fairly consistently hit and possibly better

Huw

Driving style, whether the vehicle is gas, diesel, hybrid, or whatever, has the greatest effect on fuel economy. Wide open throttle acceleration has a pretty big negative effect, as does speeding up and slowing down. Many short trips will result in poorer economy than long trips at steady throttle.

Next comes road and traffic conditions, powertrain condition, and then tire inflation.

Not disagreeing with you on any point but his car is a modern direct injection common-rail diesel which should easily achieve over 50mpg on an average out-of-town run. Now he might just drive in a gridlocked town environment for all I know and the normal average speed could be 10mph or less with frequent stops, in which case he gets about the expected mileage.

Huw

I confess that I am not very familiar with modern direct injection diesels, other than what I've read. Unfortunately, they are not common in the U.S., probably because the U.S. consumer still pictures cars belching black smoke.

I guess the bottom line for the OP is to bring the car back to a qualified service facility to be checked out.