Welcome to JustAnswer.com! My name is DriveFast71(Ron) and I will do my best to answer all of your questions completely and accurately.
Can you try something for me?
Get in the vehicle, and close all the doors. Without starting the engine, cycle the key: ON-OFF-ON-OFF-ON - within 5 seconds. Where the odometer is, there should now be displayed "p-codes" - may I have these?
K. Thanks. It'll helps us a ton in the diagnosis...
When the "gas cap" message is displayed, this actually means there is a problem in the EVAP (emissions control ) System. The gas cap is the most common problem, however, not always the case. That's why we had to do a little digging to obtain the "p-codes".
Now- both of these codes are point to an "EVAP Small Leak Detected" - make sure the fuel cap you replaced the original one with meets or exceeds Chrysler specs (for example, if you got the cap at say, AutoZone, it is far BELOW specs, and will not seal the system correctly). Make sure there are no visble defects on the cap or the filler tube that can cause the cap not to seal.
If this checks ok- next we need to look into the EVAP Purge Solenoid. Inspect the lines going to this solenoid for any cracks, holes or loose/missing connections. Inspect the solenoid for proper operation. The solenoid attaches to a bracket near the radiator on the passenger side of vehicle.
If this checks ok, the next best, XXXXX XXXXX way to diagnose this is to have the EVAP system "smoked". This is where a machine forces smoke through the system, and the "small leak" will reveal itself.