Ford Mustang: “Check Fuel Inlet” Causes

Check Fuel Inlet Ford Mustang

“Check Fuel Inlet” is one of the most common warning messages that the Ford Mustang will produce.  Really, what this message means is check the fuel cap.  More than likely, it hasn’t been secured.  It will often show up even though the fuel cap appears to be on and secured, that’s what this article aims to address.


“Check Fuel Inlet” Meaning

The check fuel inlet indicator means that the ECM has detected a pressure leak in your Mustang’s fuel tank.  Far and away the most common reason for this problem is that the fuel cap itself is missing, not tightened enough, or damaged in some way.  It sends the check fuel inlet message for you to check the most likely place that it would be leaking, the fuel inlet/cap.

If this has happened to your Ford, make sure you put the cap back on someplace safe.  There is no immediate danger, and therefore no reason to pull off the road someplace dangerous to do this.


“Check Fuel Inlet” Symptoms:  Ford Mustang

Your Mustang will still run and drive just fine.  The only thing you may notice is the slight smell of fuel (particularly if your tank is full).  If you do smell fuel, that confirms that the check fuel inlet message is accurate.  If it was snugged down, replacing the fuel cap would be the most likely fix.  They are very affordable (usually around twenty bucks).


“Check Fuel Inlet” Causes

Most of the causes related to the check fuel inlet message are going to actually be issues with the gasl cap itself.

A bad gas cap is one of the top reasons people smell gas coming from their vehicle

Gas Cap Issues

  • Missing Fuel Cap– This often happens after a fill up.  With no fuel cap on the message will populate right away.  Replacing the fuel cap will clear the message.
  • Loose Fuel Cap– When tightening a fuel cap, it needs to be tightened until there is a satisfying click.  If that click is no longer being felt, it is time to replace it.
  • Bad Fuel Cap– There is a rubber seal in the gas cap that snugs against the fuel inlet.  If this gasket has gone bad the fuel vapor will be able to escape through the cracks and the “Check Fuel Inlet” light/warning message will appear.



Your fuel tank is part of your Mustang’s larger Evaporative Emissions Control (EVAP) System.  There is a certain amount of pressure in the tank.  This pressure is secured by the fuel cap.

Your Ford’s computer will throw the “Check Fuel Inlet” warning when it detects that the pressure has changed enough that it’s likely that there is a gas cap leak.  Otherwise, it would have thrown an EVAP related trouble code (most likely P0457).


“Check Fuel Inlet” Fix

Check to make sure that the fuel cap is tightened.  If it was loose, you’ll need to snug it.  It may not immediately turn off the fuel cap warning.  Drive your Mustang for a couple days.  

If it still does not clear you should inspect the gas cap for any damage.  Take a good look at the O-ring.  If it is missing or damaged, replace the cap.

If the gas cap is OK and the message is not going away there is likely a leak in the EVAP system.


How to Check the Fuel Cap

  • Open the Mustang’s fuel door.
  • Twist the fuel cap to the left until it disengages from the fuel fill nozzle.
  • Put the cap back on.  Make sure the threads are lined up correctly and twist to the right until there is a click.


Is it Safe to Drive With “Check Fuel Inlet”?

It is safe to drive with the gas cap light on.  In fact, it’s a lot safer than pulling over to the side of the road.  Your Mustang has a built in flapper valve that will keep the fuel in the tank even if the cap is entirely missing.


Conclusion:  Ford Mustang “Check Fuel Inlet”

Gas caps can and do go bad.  They are not made to last the entire life of the vehicle (although some often do).

The check fuel inlet warning is almost always caused by a bad or loose gas cap.  It sometimes can indicate an EVAP leak.  If there is anything that you could add to help the next person reading this article, please leave a comment below.  Good luck!