The first thing to have checked is a stuck open thermostat. If the engine doesn’t come up to full operating temperature the computer will believe the engine is still cold and stay in the open loop mode.
If the thermostat checks out okay, then the next thing to check is a defective coolant temp sensor for the computer. If the sensor has failed where it’s telling the computer the coolant never gets to operating temperature when it actually does, the computer will believe the engine is still cold and stay in the open loop mode.
In both of these cases the engine will use more fuel.
Tester