Hyundai Repair: CEL code 0442, emission control system, fuel cap

Question
Hi,  00 elantra with code 0442.  Evap emission control system small leak detected.  Where do I start looking first. Is there a sensor somewhere that I can check or maybe an evap canister failing.  Can you tell me where to look.  I am a pretty good mechanic.  Thank you.   Paul H.

Answer
Your problem could be anything from a loose fuel cap to a leak anywhere in your evaporative system.  Before doing a leak diagnosis, it's probably easiest to check the fuel cap to make sure it's installed properly and clear the light and trouble code.  If the lamp and code don't come back within a week, you can probably chalk it up to a loose fuel cap at some point.

If the code insists on returning, then you may want to start checking for leaks.  There are two commonly methods for diagnosing the system.  Both involve energizing the canister close valve to seal the system and then pumping pressure into the fuel tank.  In one method, the tank is pressurized with smoke and the vehicle is inspected visually for the smoke exiting.  In the second method, the technician uses a sensitive listening device to detect escaping air.

I've never had much luck with the smoke method, and I cannot recall using the listening method.  The dealer's scan tool provides the capability of forcing the evaporative leak test to run.  With this capability, the dealer technician can see whether the leak is currently present.  If so, the technician can block different portions of the evaporative system at the appropriate time while the test is running to narrow the area where the leak may be.  If the leak is intermittent, then it's almost certainly caused by the canister close valve, since that's the only moving part that can cause a leak in the system.