2009 MKX 3.5 check gas cap light issue with intermittent check engine light with P0455 Replaced gas cap. Lights were off. Got fuel a few days later and gas cap light came on the next day. It stayed on for a week and went out. Check engine light came on 2 days later with a P0455 code. Cleared light and all was good for a week. Check engine light returned and I cleared it again. Light was off for a few days and returned a day after getting fuel. Ive checked the purge valve by disconnecting the line and the wiring harness and running the car. It had no vacuum and I believe that means its good.    I do have a smoke machine and tried smoking the fuel filler pipe. Checked underneath and didn't seem like and smoke was escaping. Having a hard time with trying to find a spot to hook the smoker to on the EVAP lines under the hood. I did try smoking the inlet line that runs from the purge valve to the charcoal canister/fuel tank. It seemed to have a leak on the passenger side in the middle? That didn't seem right to me.  Has anyone had the gas cap light/ check engine light issue like this? What was your fix for it? Thanks in advance

YES   Try fixing the caps-lock.

If you check Lincoln app, it confirms fix is available and implies it could be OTA.

I did pull the drive shaft and the axle shafts on the RDU,  left the RDU unit installed, electrical connection connected, everything seems to be working just fine, no warning lights on the dash, I basically have a front wheel drive now. Hope the PTU stays good I change fluid every 15,000. I hated to do it but since ford is building junk these days and not backing their product i guess i had no choice, after buying a brand new RDU from ford and it goes bad in one year and eight months, definitely not any different than the Chinese junk

REAR AXLE BEARINGS , THEY CLAIMED FRONT OR REAR ( KUSATEC ) AXLE . MY CAR IS FWD . THESE ARE NOT SEALED , IS THAT BAD , OR WILL THEY GET DESTROYED . ???  

OEM valve?    If yes, believe I'd smoke the vac lines again, may have caused a crack or something. 

When you fill up, do you try to squeeze ever last bit of gas into the tank?  You know, keep pumping and clicking until you can't get anymore in?  If so, this may be contributing to it.  I didn't believe it was so until I tested it out, not putting anymore gas in after the initial shutoff.  Sure enough, no fumes.  Then I tried to pump as much as I could in on the next fill up, and yep.  There were the fumes again.  So I verified that this was an issue.  This was in my previous car (a Dodge Charger), but I did try it in my Edge also, and it sure enough happened then also.  So I no longer pump until my hand cramps.  After the pump shuts off the first time, I hang it up and carry on.   If you are not doing this, then that's all I got.  

This video describes what I'm experiencing.      

From what you describe I'm guessing yours was evident at specific speeds - mine is only there at a specifc speed range (55 - 65 mph) AND accelerating - light throttle just cruising at any speed has zero vobration.   Tomorrow (11/1/25) around noon I'll have new tires on but don't expect any change to this issue.   On Saturday afternoon or Sunday I'll get in up on four jack-stands, and front wheels off, then scrutinize all potential areas such as the lower control arm buses - if its that I get the complete  lower control arms. Should I stick with Motorcraft or are Moog and Mevotech acceptable?   https://www.rockauto.com/en/catalog/ford,2017,edge,2.7l+v6+turbocharged,3434543,suspension,control+arm,10401

I thought so too. I put a vacuum gauge on the solenoid and it wouldn’t hold vacuum until I covered the outlet. I put a new one (tested to make sure it was closed and it worked) cleared the code and about 15 miles later light came back on.