What do I do to fix Check engine light? See Below. on 2005 Chevrolet Avalanche 1500

Notice of "check Gas cap" came up dashboard Tuesday. Gas cap was tight. Repair shop Cleared code - light went out. On Wednesday check Eng light came on. Replaced Gas cap. Repair shop Cleared code again- light went out. On the way home light came back on again. Diagnostic meter says "Emission Sensor Valve" Both times -->i believe was the Code name when they told me to tighten and/or change the Gas Cap which neither worked. Any suggestions?? What & where is the Emission Sensor Valve??

by in Chesapeake, VA on August 27, 2012
3 answers 1 comment
ANSWER by on August 27, 2012
The evaporative emission system has a small leak usually it is the fuel cap. It seems like the cap being the problem has been eliminated. A good repair shop should be able to perform a smoke test to find the source of the leak. The canister vent valve is a common failure item on the avalance.
COMMENT by on September 07, 2012
Canister vent valve ended up being the fix for my problem. Light went out 2nd or 3rd start-up after that. Thank you for your help.
ANSWER by on August 27, 2012
YOUR EVAP SYSTEM HAS A LEAK YOU NEED TO HAVE IT DIAG IT COULD BE 1 OF THREE SYSTEMS CAUSING THE ISSUE AND OF THOSE THREE IT COULD BE EVVN A BAD HOSE. HAVE SMOKE TEST DONE TO DETERMINE IF THERE IS A LEAK
ANSWER by on August 27, 2012
get the specific code(s) from them (if not already listed on your reciept) and post it here , maybe some one with GM experience with it can help get you in the right direction. AND possibly get references for a different shop ?
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