MPG on Gauge Inop

I have a 2007 225 and just recently the MPG function stopped working. When I first got it, it didn't work at idle speed, which I read is normal, but it worked great above that. I started to get intermittent where it would go from 2.2-2.3 and then all of a sudden drop down to .9 or 1, but after I shut down and restarted it would be fine. Just recently it stopped working at any consistency, and when at cruise speed, I just get -- where it normally reads. I know some may consider it frivolous, but I would like to get it working again unless its in the gauge and going to cost me a bunch just for that.

Make sure you have 12v between the blue/yellow and black also check the gray wire .Iam not sure which MPG gauge you referring to miles/gallon gauge[petrol gauge] or manual pulse generator[tachometer] so i put the colors for tachometer for you.

Is you speedo working? If not you economy will not work. Does show gallons per hr? I am assuming this is a genuine Honda digital gauge?

To expand on what Ian said - on the lower leg of your engine, you will find a very small hole. This operates a pitot for measuring your speed, thus your MPG. They get easily clogged. Many folks, like me, plug the hose coming from that pitot where it exits the engine and connect up an external pitot sensor on the transom. If that stops working, then it's a $10.00 replacement.