"Check Gas Cap"?

[dtwphaeton]

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?

[jkramer]

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.

[rjlvw]

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.

[PanEuropean]

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

[dtwphaeton]

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

[PanEuropean]

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

[trekguy]

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.

[guybguy]

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

[PanEuropean]

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

[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

[viscount]

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

[chrisj428]

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.

[copernicus0001]

Chris,

Any news regarding a patch??

Doug

[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.

[PanEuropean]

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

[dcowan699]

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.

[PanEuropean]

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

[car_guy]

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.

[brosen]

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

[PanEuropean]

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

[brosen]

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.

[brosen]

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 ??

[brosen]

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