hey all, my gas cap light keeps staying on in my truck. i went to autozone and said start with replacing the cap. which i did. they reset the computer and NO LIGHT came on. great its fixed........not so fast! it came on again and went back to have them reset it, they did, and no light came back on. did this process a couple of times. well its back on and evidently the new gas cap didnt do crap. now the check engine light is on... what the heck do i start replacing next?!?! i really dont wanna go to a dealership..help!! its an 04' f250 with the 5.4 motor in it. any input would help out. thank you---ryan

 

The system gets a quick vacuum to test the cap/seal. If the cap is good, I would look for a vacuum leak else where. Probably near the solenoid that closes off the canister or the vent hose it uses.

 

thank you Reax!! i'm gonna check 'er out. you saved me tons of money and time with your advice in the past. haha

 

Just for a side note, I have a Stant locking fuel cap. It doesn't always lock in like it should. I smelled gas after driving out the shooting range yesterday, and sure enough the cap was loose. I never got the light (the bulbs does work for it), so maybe the aftermarket/locking caps have a better seal or you have a bad sensor/solenoid/hose.

Stant caps should be under $15 if your interested in that route.

 

Hey I have the same problem as 78 fordtruckguy. Where is the solenoid that closes off the canister or the vent hose it uses? My gas cap light and check engine light are on also and i am trying to avoid going to a dealership.

 

I had the same issue on my 2004 SD as well when I replaced my stock cap with an locking cap. Sometimes the cap would seal fine, other times I would get the stupid light.

I ended up switching back to the stock cap. Things were good for a week or so then the stupid light and engine light came on! I messed with the cap for a few days, and then deceided to try moving the seal on the cap down some. To my amazement the lights went off in minutes of driving down the road!

The light didnt come back on for almost a month. Then all the sudden (just a few days ago actually) the engine light came on but not the gas cap light. I havent checked the code yet, but Im willing to bet its the same stupid code for a vapor leak in the fuel system. I have moved the seal again, but that didnt fix the problem.

long story short... check the seal on the gas cap. check where the cap seals to the neck for cracks.

good luck, keep us posted. I have to wait till the weekend for daylight to check mine out again!