# "Check Gas Cap"?



## dtwphaeton (Sep 7, 2004)

This morning I received a warning chime and the message "Check Gas Cap" in the driver information display. The message shortly disappeared but a warning icon remained. I shut off the engine, removed and retightened the gas cap, and restarted but the warning reappeared immediately. After uttering an expletive, I went on my way. Shortly thereafter I stopped for coffee. Apparently the car liked being shut off for a while ... upon re-start ten minutes later, no warnings. I had fueled the car Friday and definitely tightened the cap several clicks -- I always do this because I know that if you don't, the OBD system on any of today's cars senses a leak and flashes the "check engine" light. I drove 180 miles over the weekend without incident; the tank was about half full this morning when the warning appeared. Has anybody else experienced this and, if so, was there any fix other than waiting for the system to "reboot" and hope it would go away?


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## jkramer (Apr 30, 2003)

*Re: "Check Gas Cap"? (dtwphaeton)*

the same identical thing happened to me last week. I turned the car off, checked the gas cap (it was already on tight), then turned the car back on and the error went away.


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## rjlvw (May 13, 2004)

*Re: "Check Gas Cap"? (dtwphaeton)*

Same thing happened to me also during first few weeks of having the car. I checked the gas cap even though it had not been touched for awhile. Warning stayed on for a bit. After shutting off the car, it went out and has not resurfaced since.


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## PanEuropean (Nov 3, 2001)

*Re: "Check Gas Cap"? (dtwphaeton)*

I wonder - just a shot in the dark here - if the common cause of all these problems is a problem with negative pressure relief in the tank, either due to the negative pressure relief valve in the cap being blocked, or due to the very tight seal between the gas flap and the bodywork of the Phaeton.
In each of the above 3 reports, the problem happened when the vehicle (and, presumably, the fuel tank) was cold - and went away once the vehicle and tank warmed up. This would affect the pressure in the tank.
PanEuropean


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## dtwphaeton (Sep 7, 2004)

*Re: "Check Gas Cap"? (PanEuropean)*

By George, I think he's got it. At least this makes more sense than anything else that I can think of. Thanks!


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## PanEuropean (Nov 3, 2001)

*Re: "Check Gas Cap"? (dtwphaeton)*

Well, if only it was that easy...
My first suggestion to owners who are experiencing the "check gas cap" warning would be to inspect the fuel overflow drain line that leads from the bottom of the filler cap area to the ground beneath the car. My guess is that this is the primary source of ambient atmospheric pressure for the fuel cap. If that line is blocked - as it could easily be from dirt, leaves, bugs, etc. - that could well be the cause of the problem, the gas cap itself is likely innocent.
The rubber seal between the gas filler flap (the cover) and the rear quarter panel of the Phaeton is very tight. It is unlikely that ambient air can enter freely through the (non-existent) gap between the gas flap and the rubber reveal.
If the fuel overflow vent line is free and clear (you can check this yourself, next time you wash the car), then the next step would be to have your dealer inspect your fuel cap, to make sure it is opening as it should to relieve negative pressure in the tank.
*NB:* When you are checking the fuel spill vent line for patency, make sure that the line is not partially blocked with dust or mud. It is pretty common in the aircraft industry to have an ambient air pressure line that is half-blocked with dust or mud - it works fine when the humidity is low, as soon as you get into high humidity, the dust/mud/dead insect absorbs moisture, swells up, and blocks the line.
PanEuropean


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## trekguy (Aug 16, 2004)

*Re: "Check Gas Cap"? (PanEuropean)*

The check gas cap warning had appeared a few times with mine as well, as mentioned in an earlier post. It actually came on in almost the exact block of travel, on my way to Starbucks for my morning coffee. After shutting off the car at the barista, and restarting it to leave, no more warnings or beepings... just the smooth and quiet ride of the Phaeton.
Therefore, I concur with PanEuropean about the pressure theory.


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## guybguy (Jul 21, 2005)

*Check Gas Cap Warning*

Have gotten this warning twice in last week. Checked the cap the first time (it was fully closed). Ignored the second time and it did not come back. Stray gremlin, or something else? Only change is colder weather. Thanks


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## PanEuropean (Nov 3, 2001)

*Re: Check Gas Cap Warning (guybguy)*

The 'check gas cap' warning is an emissions related message. It implies that the tank cannot be pressurized (slightly), therefore, the most probable cause is a loose gas cap.
You will sometimes get this message if the air temperature around the car changes greatly, and this results in a slight negative pressure in the fuel tank.
I think you can safely ignore it.
Michael


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## dcowan699 (Nov 22, 2004)

*Re: Check Gas Cap Warning (PanEuropean)*

This too happened to me about this time last year and has not happened again. Now that I posted this and we are now experiencing cold weather, it will probably happen again


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## viscount (Jan 2, 2005)

*Re: Check Gas Cap Warning (dcowan699)*

And along the lines of winter weather, the reformulated winter gas mix is again causing the same problems with starting as seen last year...I spoke with the ever polite Diane today at customer care and she said there was a patch for this, but still hadn't been released...this is the same story I had last year....







...hopefully they can get it resolved!!!
Ed


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## chrisj428 (Feb 26, 2005)

*Re: Check Gas Cap Warning (viscount)*

Ed,
We have an Owner who is experiencing the same problem as you are with the winter blend fuel in this market. 
While I don't want to say too much (I ran my mouth enough in the Adrian Hallmark thread a few minutes ago







), I _can_ tell you that I should know very soon if the beta test we are performing right now will be successful. 
If it is, new software for everyone! I'll report as soon as I know.


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## copernicus0001 (Nov 30, 2004)

*Re: Check Gas Cap Warning (chrisj428)*

Chris,
Any news regarding a patch??
Doug


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## dcowan699 (Nov 22, 2004)

*Re: Check Gas Cap Warning (dcowan699)*


_Quote, originally posted by *dcowan699* »_This too happened to me about this time last year and has not happened again. Now that I posted this and we are now experiencing cold weather, it will probably happen again









You guessed it, Saturday or Sunday (can't remember which day) my _Check Gas Cap_ light came on. Today it has finally stayed off. It started when we had a cold snap (around 30 degrees last weekend). The weather has moderated a little since then. It seems to happen once or twice at the first of the winter months , then never comes back on. Hopefully this holds true for most of us.


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## PanEuropean (Nov 3, 2001)

*Re: Check Gas Cap Warning (dcowan699)*


_Quote, originally posted by *dcowan699* »_This too happened to me about this time last year and has not happened again. Now that I posted this and we are now experiencing *cold weather*, it will probably happen again 

Alabama definition of cold weather: It is no longer necessary to keep the house air conditioner running 24 hours a day...
Michael


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## dcowan699 (Nov 22, 2004)

*Re: Check Gas Cap Warning (PanEuropean)*

We need a good snow!! We have not had a decent winter in several years. I just spent $700 on a new A/C compressor. The coils were totally rusted and freon was going out of the roof. I had a $600 power bill as a result








Back to the subject. Didn't we also discuss a blockage of a tube that extends downward from the gas tank area down to the ground? Seems that this blockage when combined with weather changes caused an erroneous message.


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## PanEuropean (Nov 3, 2001)

*Re: Check Gas Cap Warning (dcowan699)*

Something interesting that is worth noting here: I merged two threads with the same topic (Check Gas Cap warning message) together - look at when the first post was made to each thread - once in October 2004, and once again in October 2005.
Bet ya a cup of coffee this topic will come up again in October 2006 (along with the flurry of TPMS warning message posts).








Michael


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## car_guy (Aug 19, 2005)

*Re: Check Gas Cap Warning (PanEuropean)*

My gas cap warning came on yesterday even though it was already tight. It went off after the car was off for a while and hasn't come back on today.
No big deal. 
I am impressed that they give so specific a warning even if it's wrong. I would have just expected the CEL going on and having to diagnose the problem.


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## brosen (Jun 21, 2009)

*Re: "Check Gas Cap"? (PanEuropean)*

Michael, when you said "inspect the fuel overflow drain line" you mean at the end of the line ?, to verifiy if you output is not blocked or inside the line from the cap to the end of it ?, thanks


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## PanEuropean (Nov 3, 2001)

*Re: "Check Gas Cap"? (brosen)*

Just open the gas cap cover flap (not the gas cap itself), and pour some water into the recess.


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## brosen (Jun 21, 2009)

*Re: "Check Gas Cap"? (dtwphaeton)*

Just got the same error today, cold morning (Minneapolis summer







) so I think that was the reason for the warning message. We will see in the afternoon.
I hope this problem will not be chronical during winter with -30F.


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## brosen (Jun 21, 2009)

*Re: "Check Gas Cap"? (PanEuropean)*

Did it, drainage was fine, no blockage symptoms, then I checked for DTCs and found 1 in the Engine ECU related to something like "leakage in the evaporative system", maybe I have a leak in one of the pipes of the fuel system ?, the DTC code was "intermittent", ideas, suggestions ??


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## brosen (Jun 21, 2009)

*Re: Check Gas Cap Warning (PanEuropean)*

Michael, yesterday and today while driving to work I got the "fuel cap" message, temperature outside was 60F and the tank was 1/4. I checked for DTCs and found the following static error:
*
16840 P0456 098
Evaporative Emission (EVAP)
Control System (Small Leak): Leak Detected [Static]
*
Yesterday afternoon while driving home the error message (fuel cap) dissapear from the cluster screen. Maybe now that I have a real error on the system (DTC) and the problem seems to be consistent, every day at the same time (I'll check the rest of the week) there are some issues within the evaporative system or emissions ?, thanks


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## Paldi (Sep 4, 2004)

Is it October already?

I got the "Check Gas Cap" message last night. Tightened cap. It was on this morning for the 3 mile Starbucks trip. Removed and reset the cap. Light still on. I decided to go put in $40.00 of gas. Motor turned over but Would Not Start. Tried twice more and it fired up at a very low RPM. I gave it a little gas and it perked to life. Check Engine was on briefly and went out. Got her parked in my garage and went in to turn on this computer to search the Forum. Then went out to give another try. She started right up! The gas cap light is off too.

Could this possibly be 10 year old battery syndrome? I have an appointment for Wednesday at VW for a look, but probably this gremlin won't return... I hope.


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## invisiblewave (Sep 22, 2008)

More likely bad gasoline! Mine sometimes does it if I put the 89 in before the 93.


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## PanEuropean (Nov 3, 2001)

Paldi said:


> Is it October already?


Hi Fred:

I checked the calendar, and it's not, but it sure feels like it. The temperatures were down to 11°C (52° American) here in Toronto last night, and that is more typical of fall than it is of August.

Hence I suspect that the 'check gas cap' message was simply a result of vapour pressure differential (expansion and contraction of vapours in the tank) arising from the rather large temperature swings we have experienced in the Northeast during the past few days... much like the original discussion at the top of the page, which dates from 10 years ago, when everyone had a brand-new battery.

Michael


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## Paldi (Sep 4, 2004)

Problem came up again last week. The check gas cap message came on and stayed on for about a day and the check engine icon came on and stayed on. I filled the tank and carefully retightened the cap. The CEL stayed on for about a week, then today the check gas cap light came on for 30 seconds and then went out along with the check engine light going out, finally.


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