Fuel use changes with weather, routes and driving style, but a persistent jump deserves attention. Start with simple factors before assuming a complicated fault.
Tire pressure
Underinflated tires increase rolling resistance. Check pressure when the tires are cold and use the vehicle manufacturer’s specification.
Short trips and traffic
A cold engine and repeated acceleration raise average fuel use. Compare similar routes rather than unrelated trips.
Extra drag and weight
Roof racks, heavy cargo and strong headwinds all affect fuel consumption. Remove unused external accessories when practical.
Mechanical causes
Sensors, dragging brakes, ignition problems and other faults can increase fuel consumption. If the change is large and persistent, the car needs diagnosis.
Bottom line
Keep the solution simple: start with the most likely cause, change one factor at a time, and observe the result. That makes it much easier to identify what actually works in your situation.