Nissan Repair: Nissan trouble codes, canister purge valve, emission control system

Question
I have a "service engine soon" trouble light. I used a OBD 2 meter and these problems came up.
1.)Evap Emission Control system purge valve C fault.
2.)Emission Control System Purge valve C fault.
3.)Emission Control System Circuit Malf.
This Nissan Sentra has 102,000 miles on it. I clear the fault but it comes back in a day or so. What do I replace to take care of problem.
              Thanks,  Jay

Answer
Two things could be the cause.  The first is a defective gas cap.  The second is the canister purge valve.  Check under the car and look for the evaporative hose from the gas tank and you will find a valve that has electrical wires running to it.  This is the vent valve for the system.  It is one of these or perhaps you have a loose gas hose.