On the 2013 Dodge Ram, when the Check Fuel Cap lights comes on and then is followed by the Check Engine Light, this can mean more than just a loose or faulty Fuel Cap. This can also mean there is a problem somewhere in the EVAP System. First and foremost however, is to check the Fuel Cap. Check the underside of the fuel cap for any cracks or signs of defects. Make sure the cap is seating correctly. If there are any doubts about the inspection of the cap, replace it. Keep in mind, you will need a cap that meets OE Specs. Those “universal” or “locking” fuel caps sold at after market parts stores do not meet OE specs, and will not seal the system correctly. Check the top of the fuel filler neck for any signs of damage or debris. If you are certain the fuel cap is good, then the next best course of action is to have the EVAP System “smoked”. The smoke machine forces smoke through the system and any leaks can then be easily seen and repaired. If the smoke test proves no leaks, then a very common fail item that can set a P0456 is a faulty Purge Solenoid. You can find the Purge Solenoid located on the lower side of the battery. Inspect for any problems with the electrical connector and wire harness and for any problems with the vacuum lines.
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