Why does it say check fuel cap and check engine light come on?
Why does it say check fuel cap and check engine light come on? it is a 2018 Ram 2500 Tradesman
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Your evaporative emission control system scavenges excess fuel vapors from your intake manifold and returns the fuel to the gas tank. It relies on vacuum in the gas tank so if the gas cap is loose it won't work.
So your system has detected an issue with your evap system which could be caused by a loose gas cap, but it could also be caused by several other issues with the evap system. Scan the truck for OBD-II trouble codes; assuming you've checked the gas cap and it's fine, the codes may point you to the source of the problem. Here in the US most auto parts stores will scan your codes for free.
Once you have the code or codes, come on back and add them to your question and we'll see if we can help you from there.
Update (05/27/25)
When I've had problems with the evap system it's been as a result of leaking hoses. On my car there were three hoses running to the engine compartment from the evap cannister under the right rear wheel inner fender and one of them connecting to the cannister itself turned out to have a leak, mainly due to simply age as far as I could tell.
That's the problem, finding an air leak in those hoses that's probably causing your engine codes. A mechanic might use a smoke machine to blow smoke down the hose and see where it comes out; you may have to rig up something like a pressurized air line into a hose then go down it with a spray bottle filled with water and a few drops of dish soap, looking for bubbles.
I was able to pin it down to one hose by disconnecting one end and plugging it, then using a vacuum tester to pull vacuum and see if it holds vacuum. That pointed me to the right one, then physical inspection finally showed the problem.
I can't say with any certainty that's your problem, but it's where I'd start looking.
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first code is PO440, Generic Permanent Evaporator Emission System.
Second code is PO456, Generic Permanent Evaporative Emission System Leak Detected (very small leak).
I have already replaced gas cap no change.
any thoughts?
@james36664 Yes, those codes are definitely what is causing your check fuel cap message and the check engine light. Have you cleared the errors to check for them coming back? It is possible an attendant (or you) didn't quite get the cap on completely one time, causing the code to come up. If that was the case, I'd clear the code and see if it comes back; if it was just caused by the gas cap it shouldn't return, if it does see my answer for where to go next.
