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Arench, Master Technician
Category: GM
Satisfied Customers: 1490
Experience:  30-years experience auto and truck repair.
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GM Yukon slt: I have a 2005 yukon 5.3 an the ck engine light

Customer Question

I have a 2005 yukon 5.3 an the ck engine light came on w code p0442 ! What would b the 1st thing 2 ck !?
Submitted: 2 years ago.
Category: GM
Expert:  Arench replied 2 years ago.
Thanks for your patience, my name is***** is an emissions system type of fault. The P0442 code means a small leak was detected in the airspace of the fuel tank and/or plumbing. The most frequent cause is a loose gas cap or a bad gas cap. Check cap is on correctly and if so replace with high quality cap from dealer or AC-Delco supplier or a Stant brand cap. Clean any debris or rust from the fuel fill pipe contact area. Clear fault code with scan tool. This fault takes two to five days to re-appear after reset if not resolved by the gas cap.Other possible causes are cracked or broken evap system hoses, sticking canister vent solenoid, sticking purge solenoid, rusty tank, metal lines or fuel filler neck. We always begin with a new gas cap before starting a more expensive diagnosis. This works about 60-percent of the time. If a new gas cap does not fix it the light will be back on in a few days. Then mechanics generally replace the canister vent valve and/or perform and evap leak test using a smoke machine as a next step.
Customer: replied 2 years ago.
What if I already purchased a gas cap 4rm dealer !? An light is on again
Expert:  Arench replied 2 years ago.
If a new quality gas cap did not fix it and you checked than it is installed correctly now then the next step would be an evap leak test using a smoke machine. In my market that costs about 150 dollars at shops that specialize in emissions. Some people would advise to go ahead and replace the canister vent valve because that is the second most likely thing to fail after the gas cap.