Check Fuel Cap

[alyssasdaddy]

Does anyone know why i would have a check fuel cap light on, The cap was tested and good, it seems all the evap lines are in good condition and still connected.

The truck is a 2002 Ranger 2WD with a 4.0 SHOC

I am about to start looking through everything to see if there is a problem somewhere.

* Fuel cap was tested at the smog shop

 

[trail B2]

My 01 taurus has had cap problems does this cap of yours have the two tangs like mine or the old screw style.My light came on bought a new one had to disconnect the battery for a minute got the light to go out.My G/F dropped it in the same month light came back on.Told her to buy the next one three months didn't happen I was at pick and pull saw a pile of them for a dollar each found one so I got the light back off.My G/Fs mother has a two tang cap on her car been out for about a year.Two tang caps are crap you probably need a new one and clear codes.

 

[alyssasdaddy]

Umm well that crappy, Ford and there wonderful ideas. Yeah i have that cap i will try that soon.

 

[Frank The Tank]

My 04 kept doing same thing..... pin hole in vent line.

Frank

 

[alyssasdaddy]

Well how did you find a pin hole in the vent line?

Anyways seems i also have a nice shiny p0125 code as well. Time to start checking the cooling system stuff. I know already that i have no leaks, the water is full i guess i need to check that stupid temp sensor.

 

[Yellowsplash]

Check fuel cap is the fuel capacity light, or aka low gas light. Has nothing to do with emissions...

 

[Big Jim M]

In my state they check the cap as part of the emission test!
Big JIm

 

[Yellowsplash]

I know....the evap system is emissions. What I am saying is the light in the dash stands for capacity, not gas cap.

 

[p38fln]

I have run my fuel down to the "E" on a few occasions and the "Check Fuel Light" doesn't come on.

The Check Gage light comes on instead. I copied this from the owner's manual for my truck:

Check fuel cap: Illuminates when the fuel cap may not be properly installed. Continued driving with this light on may cause the Check Engine warning light to come on, refer to Fuel filler cap in the Maintenance and Specifications chapter.

 

[kimcrwbr1]

Unless there is a micro switch on the cap itself the only way it could tell if the cap was not on would be a pressure switch or I would guess it uses the vapor collection system to put a neg pressure (vacuum) on the fuel tank at a fixed pressure so I would guess looking at the vapor lines from the fuel tank to the cannister and the vapor control solenoid is where I would be looking if the check valve in the cap is working it will pass the emission test I dont believe they test the amount of air it allows to enter the tank just that it is not leaking gasses out. That just gives me something to look into I wouldnt think the tank is under pos pressure so it must be a neg pressure switch in the tank that tells the light when to come on. Can someone tell me if you just turn the ignition on without starting the engine does the fuel cap light stay on. curious

 

[p38fln]

Edit again:
Found all the information you could ever possibly need on how this light works.
Ford 2003 OBD Operation Summary <-- Link to manual on Motorcraft site
Page 20 gives a good description

Very quick suammary -
It's based off vacuum. It tries to pull a 7" vacuum pressure in the fuel tank. If it can't, it turns on the Check Engine light with a code of P0455 (Large leak). If the tank has been refilled and then the test fails, it turns on P0457 instead - this DTC turns on the check fuel cap light instead of check engine.

 

[alyssasdaddy]

In my state they check the cap as part of the emission test!
Big JIm

Yes they check all that here too and its a dyno smog test, But last time they ran it it past about 4 months ago.

I know....the evap system is emissions. What I am saying is the light in the dash stands for capacity, not gas cap.

I think you should read up on that here, Because it is part of the emissions system, The evap system and California is very strict on the smog, evap fails so does your car. But i have run on low fuel and had it come on but i do not think it has anything to do with fuel level. That would be the check gauges light.

I have reset the light, and filled the tank so far no light.

Very quick suammary -
It's based off vacuum. It tries to pull a 7" vacuum pressure in the fuel tank. If it can't, it turns on the Check Engine light with a code of P0455 (Large leak). If the tank has been refilled and then the test fails, it turns on P0457 instead - this DTC turns on the check fuel cap light instead of check engine.

Well then the less fuel the more vacuum needed to to reach 7# if there is a slight leak i am sure this would trigger the light. Still there is a problem and i do plan on fixing it, My 94 fails smog because of that damn filler tube.

 

[Frank The Tank]

I found the hole by overfilling the hell out of my tank, until it was just barely not running out the side.

Frank

 

[alyssasdaddy]

I found the hole by overfilling the hell out of my tank, until it was just barely not running out the side.

Frank

Well i guess that would work, I on the other hand created a leak test system with a bucket, bicycle pump, and some pvc cabs and pipe and of course a schrader valve. No leaks, now i have a full tank and i am waiting for the light to come back on.

I have also checked all vacuum lines and they all look good.

So far no light.

 

[Frank The Tank]

Well i guess that would work, I on the other hand created a leak test system with a bucket, bicycle pump, and some pvc cabs and pipe and of course a schrader valve. No leaks, now i have a full tank and i am waiting for the light to come back on.

I have also checked all vacuum lines and they all look good.

So far no light.

I didn't get too fancy, just improvised.... I'm like an RBV McGyver!!!!

Frank