Three days ago the CEL came on when I started the vehicle up leaving for work. The
CX-9 ran fine and is still running fine today from what I can tell just a driver. I went to an auto parts place nearby yesterday and got the code looked up for free and it is P0451:
http://engine-codes.com/p0451_mazda.html I ordered a Scan Gauge II two days ago and should have it sometime next week. I'm on the fence as to should I take it in to the dealer or wait until my scan gauge comes in and reset the code with it and then see if it comes back. It is a 2011 and has 22,500 miles on it.
Intermittent nature indicates a failure in progress. Wires and connectors love to fail intermittently before their final complete failure. Not uncommon. No one can diagnose without having your vehicle but based solely upon what you just indicated as a symptom, it could be time to replace the Fuel Tank Pressure Sensor which is physically going to be attached to the fuel tank itself. Or, it could be something as simple as you leaving the fuel cap improperly sealed after your last fill up at the gas station by accident and the EVAP system 'detects' that as vacuum leak (though you make no reference to DTC P0446 which is common for EVAP Vent System Failures).
With P0451, the very first thing you can check on your own is the fuel cap - is it properly sealed. Sometimes the fuel cap is properly sealed but just worn out and needs to be replaced - especially if it has a history of not being secured or sealed properly. There have been reports of people simply replacing their fuel cap and disappearing the check engine light along with P0451.
1) Remove and re-seal fuel cap
2) Delete P0451 using your Scan Tool
If the code does not return, you have more than likely solved the problem. If the code returns, you obviously have more troubleshooting to do.
Your FTP sensor has three wires. One of those wires sends a reference voltage signal to the ECU/ECM (typically up to 5 volts) which it uses to function the EVAP monitor (your FTP is part of your EVAP system). That wire, or one of the other two remaining wires (5v wire or Ground Wire) could be bad, but you would need to conduct a proper voltage test to determine this. The FTP sensor is also connected to your fuel tank via hose as well and it should be checked for cracks and wear. A Seal & Purge Test may need to be run on your tank which checks the EVAP Solenoid and FTP sensor function - whether or not they are working together properly. Electrical circuit function to and from the FTP sensor and EVAP Solenoid would be revealed as well as EVAP Solenoid valve function. Something your mechanic will probably have to do - unless you have or obtain the right Scan Tool and are willing to learn how to use it to initiate the troubleshooting sequence.
I don't know where the FTP sensor is located on your vehicle exactly, but if you can reach it without dropping the tank it would be possible for you to learn how to run your own voltage diagnostic on the unit using a simple multi-meter. If you don't feel comfortable learning how to do that, or can't reach the unit given its location, then taking it to certified/trained/experienced mechanic is probably no doubt the best thing to do.
It is great that you at least pulled the code - took the right first step. That gives you a basic or general reference on the starting point for solving the problem and it enables you to at least talk with your mechanic about it. This unit should not effect drive-ability. That's why you got a DTC without problems from the vehicle. At the same time, you don't know of the other components within the EVAP system are causing this particular DTC to emerge suddenly.
Run the fuel tank cap check. That's the easiest thing you can check on your own. Report back if you can. I'd like to know how this turned out for you.