2004 Avalanche 5.3L Z71 - Black, 120,000 miles
I had been experiencing a P0446 Evaporator Vent Control Circuit engine code for a while along with trouble filling the gas tank. When filling, the gas pump (independent of filling station) would shut off after only a couple seconds of filling. I tried all the tricks, including holding the gas pump hose at a 90% angle, etc. - with limited success. Initially, in 2012, I replaced the vent solenoid (ACDelco 214-2149 Professional Vapor Canister Vent Solenoid) which is located under the truck in front of the gas tank - this provided some marginal improvement for a short period of time. I lived with the problem and spent a bunch of time searching the forums for the magic solution. Recently, I decided to try to resolve the issue and replaced the canister purge valve (ACDelco: 214-1105 GM Original Equipment Vapor Canister Purge Valve) which sits under the cover on top of the engine. This did not solve the problem. Next, I concluded that it was likely an issue with the vapor canister (ACDelco: 22963841 GM Original Equipment Vapor Canister), so I purchased one and swapped it out. The new vapor canister resolved the issue and I can now fill up without the pump shutting off every 3 seconds. I cleared the P0446 code and it has been several weeks and it has not returned.
Notes:
1) I could still force air through the original vapor canister - but did feel that there was some additional back pressure compared to the new canister
2) I have also read info that says to not `top-off' your tank when filling up - it's possible that topping off may have contributed to the problem with the vapor canister.
PROCEDURE TO REPLACE THE VAPOR CANISTER
LOCATE VAPOR CANISTER UNDERNEATH IN FRONT OF REAR AXLE NEAR GAS TANK. IT'S A LARGE BLACK PLASTIC BOX, MEASURING APPROXIMATELY 13" X 10" X 5" IN SIZE. REMOVE THE TWO LARGER HOSES (ONE INPUT FROM FUEL TANK AND ONE OUTPUT TO VENT SOLENOID) BY SQUEEZING HOSE CONNECTOR AT BASE (NEAR CANNISTER). SLIDE VENT SOLENOID ASSEMBLY OFF OF ITS BRACKET AND MOVE ASIDE (YOU CAN REMOVE ELECTRICAL CONNECTOR IF NECESSARY). REMOVE TWO (13 MM) BOLTS HOLDING VAPOR CANISTER BRACKET TO FRAME AND LOWER DOWN TOWARDS GROUND. REMOVE ONE (13MM) BOLT HOLDING CANNISTER TO BRACKET. YOU MUST REMOVE THE CANISTER FROM THE BRACKET TO BE ABLE TO GET A GOOD VISUAL AND READILY REMOVE THE LAST (SMALLER) HOSE CONNECTOR (GOES TO PURGE VALVE) BY PINCHING CONNECTOR. HAVING CANNISTER LOWERED PROVIDES BETTER ACCESS TO THIS SMALLER HOSE CONNECTOR. REPLACE CANNISTER AND REASSEMBLE IN REVERSE ORDER.
While I likely didn't need all of these parts, the first two were relatively inexpensive and simple to replace, making it not too costly to use a process of elimination.
ACDelco: 214-2149 Professional Vapor Canister Vent Solenoid ($12 on Amazon)
ACDelco: 214-1105 GM Original Equipment Vapor Canister Purge Valve ($15 on Amazon)
ACDelco: 22963841 GM Original Equipment Vapor Canister ($92 on Amazon)
Hope that this is helpful.
---thrasher