Hyundai Repair: Purge Control Valve, gasoline vapors, fuel vapors

Question
What does the purge control valve do?  Why does the car work just fine even if it is not working?  Is there any need to get it replaced?  Talking abot a 2005 Hyundai Elantra.  Thank you.

Answer
In your fuel tank, you have gasoline and gasoline vapors.  If the system were completely sealed, the gas tank would build pressure or vacuum as the temperature changes.  This could be easily be remedied with a venting gas cap, which was in fact what older cars used, but federal law prohibits the release of gasoline vapor into the atmosphere.  So vehicle manufacturers needed to develop a system to manage the fuel vapors.

Taking advantage of the fact that charcoal absorbs fuel vapors, you vehicle is equipped with a plastic canister with charcoal pellets in it.  One end of the canister then vents to atmosphere where fresh air can be sucked in as necessary.  The presence of the charcoal prevents the vapors from being released.  The other end of the canister is connected to the intake manifold of your engine through a solenoid valve (called a purge control valve) controlled by the engine control module (ECM).  Under certain driving conditions, the ECM will open the valve, allowing the engine operation to suck the fuel vapors into the intake and burn them as part of the engine operation.

Whether you'll need to replace the purge valve will depend on how it has failed.  If it's stuck open, you may have difficulty starting your engine after refueling.  In the event of such a failure, when you fill your fuel tank, you'll be forcing the fuel vapors into the engine, creating a flooding condition.  If the purge valve is stuck closed, you're unlikely to see any negative effects.  

I would expect that your check engine lamp is on or will come on due to the problem you have with the purge valve.  If you're in an emissions attainment area (mandatory vehicle emissions testing), this will likely cause you to fail the emissions test.  In addition, if the check engine lamp is on and another problem develops, you'll have no way to know that you have an additional problem unless you just happen to scan for codes and find additional codes.