u/tominhhoang

My family bought the car brand new from the dealership when it came out. We has kept up with maintenance every year. We recently notice a full tank of gas used to net us >500km. Now, a full tank only get us ~322km. The reading say it takes 17.1 litres per 100km, so ~13 mpg, which is significantly lower that the average i can find in this subreddit previous posts. When I brought this up with the service person, after maintenance, he said everything checks out, nothing out of the ordinary. I drive in the city at ECO mode exclusively. Would someone be able to advise what is the potential issue? Thank you!