2005 Tahoe/Fuel filling problem

[OR VietVet]

Be careful in the future to not top off the fuel after the first click or so. Overfilling the tank can saturate the charcoal canister.

Yea, I always say, "Do not top off".

 

[RET423]

Whenever the nozzle kicks off when there is plenty of room for gas it means that the air being displaced by the incoming fuel cannot escape quickly enough, in the old days the air displaced when fueling was simply vented to the atmosphere via a vent on the tank; since the emissions era this displaced air (fumes) are supposed to be captured before they reach the atmosphere.

This is done with 2 strategies on your 2005, the first is the evap cannister connected to the fuel tank; the fumes travel via a hose to this cannister which absorbs the fumes until the engine is started and uses vacuum to draw those fumes into your combustion chambers via the intake manifold.

The second system is a secondary path from the tank to the rubber seal on the fuel filling nozzle, this is usually an external hose from the tank to the fill pipe above where the nozzle will be injecting the fuel; so the fuel goes into the tank and excess air/fumes return back into the fill pipe from your tank via this hose and get captured by the nozzle gasket.

On your vehicle the displaced air/fumes cannot exit fast fast enough so the tank is quickly pressurized and the fuel splashes back on the nozzle trip coil to prevent spillage.

Since the vast majority of the fueling air displacement is handled by the tank to fill pipe vent hose I am certain that yours is restricted, but the check gas cap (which is a small leak evap code) means that your evap system is not maintaining as much vacuum when the engine is running as it should; it is not a major leak so it asks you to check if the gas cap is loose or worn out (they rarely are) before you begin the grueling process of looking for a tiny vacuum leak that literally could be anywhere in the fuel system.

To get it fueling again focus on that tank to fill pipe vent hose, if you are lucky that restricted line will also be the small vacuum leak and both problems will be fixed once you get it cleared out and the hose replaced

 

[Tahoe97]

Whenever the nozzle kicks off when there is plenty of room for gas it means that the air being displaced by the incoming fuel cannot escape quickly enough, in the old days the air displaced when fueling was simply vented to the atmosphere via a vent on the tank; since the emissions era this displaced air (fumes) are supposed to be captured before they reach the atmosphere.

This is done with 2 strategies on your 2005, the first is the evap cannister connected to the fuel tank; the fumes travel via a hose to this cannister which absorbs the fumes until the engine is started and uses vacuum to draw those fumes into your combustion chambers via the intake manifold.

The second system is a secondary path from the tank to the rubber seal on the fuel filling nozzle, this is usually an external hose from the tank to the fill pipe above where the nozzle will be injecting the fuel; so the fuel goes into the tank and excess air/fumes return back into the fill pipe from your tank via this hose and get captured by the nozzle gasket.

On your vehicle the displaced air/fumes cannot exit fast fast enough so the tank is quickly pressurized and the fuel splashes back on the nozzle trip coil to prevent spillage.

Since the vast majority of the fueling air displacement is handled by the tank to fill pipe vent hose I am certain that yours is restricted, but the check gas cap (which is a small leak evap code) means that your evap system is not maintaining as much vacuum when the engine is running as it should; it is not a major leak so it asks you to check if the gas cap is loose or worn out (they rarely are) before you begin the grueling process of looking for a tiny vacuum leak that literally could be anywhere in the fuel system.

To get it fueling again focus on that tank to fill pipe vent hose, if you are lucky that restricted line will also be the small vacuum leak and both problems will be fixed once you get it cleared out and the hose replaced

Again, great insight. After all the work GMC did to address this issue described earlier, we started having some issues with stalling and rough running plus our Tighten Gas Cap message continued when first starting up. Two codes were picked up, one indicating a malfunctioning fuel tank pressure sensor and the other indicating misfiring. So new wires and plugs plus a replacement of the pressure the sensor was done and we are running smooth again, able to fill the tank without any issue, BUT the Tighten Gas Cap message occasionally comes on shortly after starting the Tahoe but rarely thereafter for the rest of the day. That continues to be a mystery.

 

[Fless]

BUT the Tighten Gas Cap message occasionally comes on shortly after starting the Tahoe but rarely thereafter for the rest of the day. That continues to be a mystery.

The test that indicates evap leaks is done only under certain conditions. For example, only on a cold start, with between 1/8 and 7/8 fuel level, the intake air temp must be within a certain range of the engine coolant temp, and the coolant temp must be below a certain temp, etc. Those aren't the only ones, and there are several specific conditions to be met in order for the test to run. So generally you'll see an issue soon after a cold start meeting those conditions, if there's an evap leak. If those conditions aren't met, the evap test doesn't run.

 

[stocksj]

Similar issue with my 07 Suburban. I'll need to check the pressure vent tube. When I try to add gas I can hear the pressure changing and the the fuel flow stops.

 

[MassHoe04]

I am frequently getting P0449 for the EVAP Vent Solenoid Control Circuit, along with fairly frequent "Tighten Fuel Cap" messages on the DIC display.

It is not Spring yet, so for now I just keep clearing them or ignoring them until they clear themselves after a few drives. When warmer weather comes, I'll see what's going on.

I have my new Tech 2, so I hope I can see if the vent and purge valves are responding and what happens to tank pressure when they do their thing.

We only have to pass safety in MA, but I am all set until October anyway.
It is just annoying to have a code popping up all the time. Even though I know it is P0449, I keep checking to make sure it is not something else.

Probably end up replacing both canister and vent solenoid when nice weather hits.

I'll get this fixed, eventually, so I can be able to tell when a real code pops...

 

[MassHoe04]

Update on P0449:

For a while, I was getting the P0449 EVAP Vent Solenoid Control Circuit, along with fairly frequent "Tighten Fuel Cap" messages on the DIC display.

While I was busy ignoring that code for a while, I started getting P0496 "Evaporative Emission System High Purge Flow".

I was not getting the 449 vent code for maybe two months, just the 496.

I checked the purge solenoid with the Tech 2. I was getting no response, so I replaced it.

I have been code free for several weeks and not getting any messages about the gas cap on the DIC either.

I think the vent code may have been related to the purge valve failure. Since the purge was just letting full flow through when it shouldn't, I think it might have been messing up what the vent solenoid was trying to do and causing that 449 error and tighten gas cap message.

My procrastination may have paid off! I was tempted to fire up the Evap parts cannon, but held back.

Seems I may have fixed both code issues with a $36 purge valve that took 5 minutes to replace.

Just thought I would document what I was seeing, in case it helps others.

 

[Fless]

Update on P0449:

For a while, I was getting the P0449 EVAP Vent Solenoid Control Circuit, along with fairly frequent "Tighten Fuel Cap" messages on the DIC display.

While I was busy ignoring that code for a while, I started getting P0496 "Evaporative Emission System High Purge Flow".

I was not getting the 449 vent code for maybe two months, just the 496.

I checked the purge solenoid with the Tech 2. I was getting no response, so I replaced it.

I have been code free for several weeks and not getting any messages about the gas cap on the DIC either.

I think the vent code may have been related to the purge valve failure. Since the purge was just letting full flow through when it shouldn't, I think it might have been messing up what the vent solenoid was trying to do and causing that 449 error and tighten gas cap message.

My procrastination may have paid off! I was tempted to fire up the Evap parts cannon, but held back.

Seems I may have fixed both code issues with a $36 purge valve that took 5 minutes to replace.

Just thought I would document what I was seeing, in case it helps others.

Here's a lesson in how to avoid the parts cannon approach by doing some easy testing.

EDIT: since it was a circuit code, you could have connected a small amperage test light and turned control on and off to verify the (wiring) circuit. Apparently your circuit issue was internal to the purge valve.

 

[rockola1971]

Whenever the nozzle kicks off when there is plenty of room for gas it means that the air being displaced by the incoming fuel cannot escape quickly enough, in the old days the air displaced when fueling was simply vented to the atmosphere via a vent on the tank; since the emissions era this displaced air (fumes) are supposed to be captured before they reach the atmosphere.

This is done with 2 strategies on your 2005, the first is the evap cannister connected to the fuel tank; the fumes travel via a hose to this cannister which absorbs the fumes until the engine is started and uses vacuum to draw those fumes into your combustion chambers via the intake manifold.

The second system is a secondary path from the tank to the rubber seal on the fuel filling nozzle, this is usually an external hose from the tank to the fill pipe above where the nozzle will be injecting the fuel; so the fuel goes into the tank and excess air/fumes return back into the fill pipe from your tank via this hose and get captured by the nozzle gasket.

On your vehicle the displaced air/fumes cannot exit fast fast enough so the tank is quickly pressurized and the fuel splashes back on the nozzle trip coil to prevent spillage.

Since the vast majority of the fueling air displacement is handled by the tank to fill pipe vent hose I am certain that yours is restricted, but the check gas cap (which is a small leak evap code) means that your evap system is not maintaining as much vacuum when the engine is running as it should; it is not a major leak so it asks you to check if the gas cap is loose or worn out (they rarely are) before you begin the grueling process of looking for a tiny vacuum leak that literally could be anywhere in the fuel system.

To get it fueling again focus on that tank to fill pipe vent hose, if you are lucky that restricted line will also be the small vacuum leak and both problems will be fixed once you get it cleared out and the hose replaced

Fill pipe vent hose restricted? By what? What on earth could possibly get in there and how?