I?ve noticed a sign ?Do Not Top Off? on some gas pumps. There?s never an explanation included on the sign and I just assumed it had something to do with gas fumes while refueling and ignored it. But topping off the fuel tank may have caused an evaporative emission system component failure on our truck.
I just got back from All Pro Tune Up in Milton, FL. (If you?re local, they?re very friendly, informative, professional, reasonably priced and appear to do good work)
The problem was a persistent ODBC P0496 code on our 2007 Avalanche LT 5.3 4WD & I couldn?t fix it. ODBC P0496 is ?Evaporative Emission (Evap) System Flow During Non-Purge Condition? or modern ?car computerspeak? for an emission system problem.
The trouble code was cleared by replacing the Evaporative Canister Purge Solenoid Valve (located near the intake manifold).
The function of the Purge Solenoid Valve is to pull fuel vapor from the fuel tank via the Evap Canister and dump the fuel vapor into the intake manifold where it is combined with the fuel flow into the combustion chambers. The Power Control Module (computer) turns the valve on and off as needed. The mechanic discovered that the valve was stuck open. I had replaced it in June and that cleared the code. Then it was stuck closed. But the code reappeared in August. Since it had only been two months I figured something else had failed, but I couldn?t find it. And it never occurred to me to test the new Purge Solenoid after being installed just two months ago.
The Evaporative Canister Purge Solenoid Valve failure may have been caused by topping off the fuel tank.
Topping off, ?packing the tank?, or rounding up to an even dollar amount during fueling can force gasoline too far up into the filler neck, which then flows into the fuel vapor vent tube located near the top of the fuel filler neck. The gasoline flows down the vent tube and into the vapor canister near the fuel tank, which is designed for vapor, not liquid. There, the gasoline dislodges the charcoal inside the canister. Particles of the charcoal are then pulled along with fuel vapor via vacuum pressure through the line to the engine compartment and into the purge valve solenoid causing it to fail. It might also cause the Evaporative Canister and/or the Evap Vent Solenoid Valve near the fuel tank to fail as well.
I don?t know how common this problem is, but due to the similarity, it could apply to Silverado, Suburban, Tahoe, GMC Sierra, Yukon and Cadillac Escalade. It also might apply to all GM gasoline powered vehicles, and possibly all gasoline powered cars and trucks period, but I haven?t looked into that yet. And I?m not sure when I will because the ?dealing with vehicle problems? section of my brain is threatening to go on strike.
The solution to this emissions system component failure problem is to stop fueling when the dispensing nozzle automatically kicks off the first time. The trouble with that is that a bubble coming up the filler neck while refueling can trip out the nozzle long before the tank is full.
So, fill your tank, but don?t top it off. Which is like saying fill your tank but don?t fill your tank!
I?m liking horses more and more?
JAG
><)))?>
I just got back from All Pro Tune Up in Milton, FL. (If you?re local, they?re very friendly, informative, professional, reasonably priced and appear to do good work)
The problem was a persistent ODBC P0496 code on our 2007 Avalanche LT 5.3 4WD & I couldn?t fix it. ODBC P0496 is ?Evaporative Emission (Evap) System Flow During Non-Purge Condition? or modern ?car computerspeak? for an emission system problem.
The trouble code was cleared by replacing the Evaporative Canister Purge Solenoid Valve (located near the intake manifold).
The function of the Purge Solenoid Valve is to pull fuel vapor from the fuel tank via the Evap Canister and dump the fuel vapor into the intake manifold where it is combined with the fuel flow into the combustion chambers. The Power Control Module (computer) turns the valve on and off as needed. The mechanic discovered that the valve was stuck open. I had replaced it in June and that cleared the code. Then it was stuck closed. But the code reappeared in August. Since it had only been two months I figured something else had failed, but I couldn?t find it. And it never occurred to me to test the new Purge Solenoid after being installed just two months ago.
The Evaporative Canister Purge Solenoid Valve failure may have been caused by topping off the fuel tank.
Topping off, ?packing the tank?, or rounding up to an even dollar amount during fueling can force gasoline too far up into the filler neck, which then flows into the fuel vapor vent tube located near the top of the fuel filler neck. The gasoline flows down the vent tube and into the vapor canister near the fuel tank, which is designed for vapor, not liquid. There, the gasoline dislodges the charcoal inside the canister. Particles of the charcoal are then pulled along with fuel vapor via vacuum pressure through the line to the engine compartment and into the purge valve solenoid causing it to fail. It might also cause the Evaporative Canister and/or the Evap Vent Solenoid Valve near the fuel tank to fail as well.
I don?t know how common this problem is, but due to the similarity, it could apply to Silverado, Suburban, Tahoe, GMC Sierra, Yukon and Cadillac Escalade. It also might apply to all GM gasoline powered vehicles, and possibly all gasoline powered cars and trucks period, but I haven?t looked into that yet. And I?m not sure when I will because the ?dealing with vehicle problems? section of my brain is threatening to go on strike.
The solution to this emissions system component failure problem is to stop fueling when the dispensing nozzle automatically kicks off the first time. The trouble with that is that a bubble coming up the filler neck while refueling can trip out the nozzle long before the tank is full.
So, fill your tank, but don?t top it off. Which is like saying fill your tank but don?t fill your tank!
I?m liking horses more and more?
JAG
><)))?>
