Focus Fanatics Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
3,487 Posts
Discussion Starter #1
Mine came on today.....it's been a few weeks since I did anything under the hood, and a hundred miles since I added fuel. I checked the cap and it was tight.

Well this is a locking cap I put on there four months ago. So I'm trying the old cap over again.

The questions....what causes the light to go off? Is it an OBDII related failure, something a code reader will turn off? And what else besides the fuel cap could set this warning light? Finally...is this warning simply a vacuum leak detected in the fuel tank system?
 

·
Registered
Joined
·
1,247 Posts
it means your cap isnt providing a good seal and if you get emmisions checks you will fail, I have had to replace mine already too.
 

·
Registered
Joined
·
3,487 Posts
Discussion Starter #3
Well obviously it could be a leaking fuel cap....but since the cap doesn't have it's own sensor, it must be using a vacuum sensor attached to the fuel tank somewhere. Which also means any small vacuum leak by a hose or seal on the tank could set off the same warning light.....

I don't have a service manual to check further....
 

·
Registered
Joined
·
1,124 Posts
I had the same problem, replaced the gas cap and voila, problem solved.
 

·
Registered
Joined
·
115 Posts
My car has this same problem, or this is a possible problem that I had. A certain part of code has to be reset, take it into a shop and it costs about $40 so it might not be worth it. It's happened twice to me.
 

·
Registered
Joined
·
1,247 Posts
My car has this same problem, or this is a possible problem that I had. A certain part of code has to be reset, take it into a shop and it costs about $40 so it might not be worth it. It's happened twice to me.
wow $40. cost me like 10 bucks for a new cap and after a while the cel went off and I passed an emmisions test no problem.
 

·
Registered
Joined
·
1,271 Posts
It could mean the cap is bad, or your just didn't put it on straight. I've had the damn light come on with a couple of other cars I've had b/c of that reason. It drove me freakin nuts.
 

·
Registered
Joined
·
115 Posts
wow $40. cost me like 10 bucks for a new cap and after a while the cel went off and I passed an emmisions test no problem.

It probably should have only been that much but for some reason the garage thought the problem was with the computer, it might have been but it messed up again just a few weeks ago so I just live withit.
 

·
Registered
Joined
·
159 Posts
More technically I believe that its when your computer detecs an evap large leak. It gives you the chance to check the fuel cap first before it turns on the CEL. So could be a fuel cap could be a evap leak caused by vent solenoid or something.
 

·
Registered
Joined
·
3,487 Posts
Discussion Starter #11
That last explanation sounds about like I was thinking.....although on most cars it doesn't need a large leak to be detected.

I'm familiar with most emission-related stuff, but not this Ford system in particular. On other cars a leak in the evap system turns on the CEL. Apparently this Ford system has this different "Fuel Cap" light that turns on when a small evap -related leak is detected. That's what it seems anyway.

I'll make a trip to Auto Zone today (where I bought the locking cap)....and see if they can check the cap and maybe turn off the light. Most of the time it's a bad cap that sets these codes....second most common failure for this code is the vent control valve (also called a vent solenoid). A really large leak in the evap system can usually be smelled. So I've got a very small leak somewhere.....hope it's just the cap.
 

·
Registered
Joined
·
288 Posts
To better understand what's going on here got to the Motorcraft web site (www.motorcraft.com) under the technical resources tab, "OBDII Theory and Operation" and download (for free) the *.pdf version of the OBD-II manual for your vehicle. In your case (2006):

http://www.motorcraftservice.com/vdirs/diagnostics/pdf/OBDSM608.pdf

Then go to the section labeled:

"EVAP System Monitor - 0.040” dia. vacuum leak check"

and read about the conditions that trigger the “Check Fuel Cap” light.

FoMoCo vehicles fly with a relatively sophisticated OBDII system and there is a wealth of information about it in these free manuals.

I've had one intermittent "Check fuel cap" light (on another vehicle) which was caused by a leaking seam in the gas tank. In that instance, replacing the gas tank fixed it.

-drjkel
 

·
Registered
Joined
·
3,487 Posts
Discussion Starter #13 (Edited)
Well thanks a lot for that Ford PDF link.....if you're willing to wade through it, the subject is discussed thoroughly. Pretty heavy though.....

Learn something new every day. The code that the "check gas cap" light set was PO447. This is described as a gross (big) leak in the evap system, rather than the small leak I was suspecting. It could be caused by a missing gas cap, or other problems.

Well I took the car to Auto Zone, and they let me use their code reader, since it was raining hard and the counter guy didn't want to get wet. Lucky....AZ won't erase codes, but I did. Afterward, I drove the car about an hour, and the code didn't return (got the OEM cap back on there). Maybe the locking cap actually is bad, and somehow left the gross leak code....hard to figure, since It was tight, and doesn't look bad. AZ can't check gas caps....but they're cheap enough to just try a new one.

If the code returns, I'll update this thread.

Oh.....if you do get that check fuel cap light, and you buy a new cap or just tighten the thing...and it fixes the problem, the light will go out by itself after driving a short time. You might have to let the car sit over-night, and do the driving after the engine has cooled. Good luck...
 

·
Registered
Joined
·
288 Posts
Delighted that your problem is solved!

-drjkel
 

·
Registered
Joined
·
3,487 Posts
Discussion Starter #15
Well the problem is not fixed.....the error code returned. This time it set the CEL, rather than the "check fuel cap" light. And the code this time is P0455.....which is a big leak in the evap system, basically the same as the previous code.

So it's off to the dealer.....my guess is the vent control solenoid, since most other big leaks in the evap system would probably be smelled. Never know...
 

·
Registered
Joined
·
3,487 Posts
Discussion Starter #16
Well my little problem here is apparently fixed......no more CELs for over a week.

Here's what the dealer told me (and charged me for of course)......The original cap that was on the car when I got it, was not a Ford cap (who would have known). The new locking cap I bought also was bad....two bad caps in a row. The fix involved me buying a third fuel cap for $34.

Hard to believe the story.....but who knows? The codes I was getting pointed to a "gross leak". Not simply a small leak from a cap, but maybe the Ford CEL system is not as "smart" as I thought it would be. Small leaks from a Nissan fuel cap, always leave a "small leak" or "very small leak" code.
 

·
Registered
Joined
·
17 Posts
I know this is a VERY VERY old thread but i have had a dilemma with my gas cap on my 08 Focus,99 Mustang Cobra, i went to a local autoparts store bought the best locking gas cap they had listed for the cars as our gas prices are getting a little steep here in canada $1.41/liter and the Cobra is $1.64/liter and i put the locking caps on then next thing i know gas cap light comes on in the focus and the CEL came on in the Mustang.Both happened after a couple months after i changed the caps and when i put stock caps on reset the computer lights went out all was good then gas prices started to creep up again and when you put 60-90 dollars in gas in i would rather have a deterrent and let the gas thief go on to the next car but everytime i put the locking cap on the focus it's good for a couple months then the gas cap light comes on and the car runs extremely bad. i finally got tired of the dealer charging me an 80 dollar fee to read the code so i spent 90 on a scanner of my own and now i can get a live feed from the car hook it up to my computer and it tells me what is wrong with the car... i figure 90 dollars well spent on my part..considering the last time i went to for they charged me 180 for a diag/sparkplug and another 85 for a pcm re-write
 

·
Registered
Joined
·
16,578 Posts
Here in Texas the inspection stations will check the cap itself for holding pressure if you are nice to them and slip 'em $5 for lunch.
 

·
Registered
Joined
·
75 Posts
Had the check gas cap light come on on my son's Focus after we put a locking gas cap on. We tried putting a thin film of oil on the gasket of the cap (like you would with an oil filter before installing) and the problem went away. I'm guessing the gasket on the cap was just a little dried out and caused a leak. Did this last fall and no problems to this day.

Best of luck.

Bob
 

·
Registered
Joined
·
16,578 Posts
Either that or the little valve in center stuck, I have cured one by sticking something up in the valve and just rocking it about.
 
1 - 20 of 20 Posts
Top