How many litres are you putting in for 400km's of driving.
Claiming 400 per tank is not accurate. For example so drive until the tank still have 1/4 tank of fuel and only 45L will go in on a fill up. Others will drive with the low fuel light on for over 50 Km's or the DTE reads 0, then fill up. Squeezing in just over 60L.
I have a similar vehicle and have seen over 650km on one tank but that was straight highway in the summer using almost all of my tank. In the winter time combined with short trip city driving it's not uncommon to see just over 400 km's per tank.
Yea 400km isn't much worse than what my 03 ES is getting city driveing. If you expect more I'd get a full tune up, plugs, ect.... Also check your tires are up around 32-35 psi, cold weather lowers the pressures and just 1 low tire can decrease your mileage a fair bit.