Sudden MPG drop, no change in driving habits or gas

Check it a few more tanks of gas. It could just be a fluke. If the problem continues, the first thing is to bring all your maintenance up to Honda specs for your car. Look at your owner’s manual for the specs.

And think of what has changed recently. Have you driven in extra-dusty areas lately? A clogged air filter for example could cause this.

After that, ask your mechanic to show you any stored codes.