P0442 describes a "medium" sized evaporative system leak, but it can vary in its actual size. By definition, it's about the size of two pinholes.
It could be something as simple as a loose or leaking gas cap. You might try sniffing around the gas door to check for odors. I pat the bottom of the door with my hand to force air into the bottom section and out the top for a better stream past the nose.
The next choice would be at the vapor canister. Slide under the truck on the left side, just about even with the driver's door latch. You'll find the vapor canister and evaporative system leak detection pump (LDP) just to the left of the driveshaft. The large (1/2" dia) hose connecting the vapor canister to the LDP cracks often. It may even fall off if the crack gets bad enough. The hose starts at the canister top, does a few changes of direction and winds up at this Jarvik-7 looking device.. the LDP. A break between these two locations will show up as a leak in the evap system, even though (technically) it's not. Everything after the canister is OK to be vented, but this is the plumbing used by the LDP for determining whether the system holds pressure. Ironic how these things work sometimes.
From there, follow the plastic tubing to the front of the truck. Some rubber hose connections between sections can still give you problems on the way to the purge solenoid, but it doesn't happen nearly as often as the large formed hose at the LDP. The purge solenoid is just to the (vehicle) right of the battery and has two hoses going to it. Everything AFTER the purge solenoid becomes the purge system and will set a different code than an evap leak DTC, so the problem has to be between the purge solenoid and the gas cap.
The tank is also part of the evap system and does sometimes have issues of this sort. You'll likely see staining on the tank sides from liquid fuel leakage if this is the case. Leaks in the tank will often let you overfill it and sets it up for this type of situation. Once again, follow your nose.
Once repaired, the MIL will stay on for up to three days afterward if not cleared. The evap leak monitor runs its test but once per day in most cases and two or three Good Trips are required to extinguish the light. Once it's gone out, you'll know that the problem is repaired.
You could do a battery disconnect to clear the code if you prefer. Then you'd be looking for the light to come back ON after two or three days to tell if the leak monitor is satisfied. Either way, you'll know by mid-week.
Write back if you have any questions.
Great! The hose costs less than $10 and is probably stocked at your friendly neighborhood Dodge dealer. I don't recall the part number, but I could get it for you Tuesday (off tomorrow). Stick with the factory replacement part. Kinks and the restrictions that would arise from using straight line will set codes of their own.
Mileage... varies. I don't actually hear much from customers these days about MPG, something that's bound to change (lol). What little I have heard puts the full-size DR truck right around 15 for combination driving. You're not likely to see 20 and I would expect it to do better than 10, but these depend upon a great many variables. The vehicle's self-diagnostic system is quite strong and will normally tell you in advance if something is weakening... not just broken.
While it won't amount to much, fixing that small evap leak means a little more fuel will go to good use instead of being vented to atmosphere. Every little bit helps.
Thanks ricky! Good luck with your Ram!