When you say your car is using a lot of gas and the “check engine” light on, leads be think your vehicle may have an O2 sensor (oxygen sensor) that is bad.
The O2 sensors that we use today were developed in 1990. O2 sensors monitor how much unburned oxygen is in the exhaust as it passes through the engine. It tells your car’s computer if the fuel mixture is burning rich (less oxygen, more fuel) or lean (more oxygen less fuel). Sounds like your car’s engine is being forced to guess how much gasoline to use; therefore, this could be why your car is using a lot of gas lately.
The actual number of oxygen sensors for a car depends on the year, make, model and engine. However, most of the later model vehicles have four oxygen sensors. Your service technician will run a computer diagnostics check. He/she will also test each sensor to determine which one to replace.