2003 F150 Triton 4.6. I keep getting a service engine soon light that comes on. I had it checked and they keep saying loose gas cap. I replaced the gas cap with an after market cap and the light returned. I ordered one from the dealership using the vin number. The same problem occurred again. It will stay on for several weeks and the gas cap light comes on then they both go off for several days then the SES light comes back on.

 

You probably have an issue with the evap system then. Do you by chance have an odor of fuel (outside the truck) after you shut the truck off?

 

Occasionally I smell gas. Not all the time

 

Yeah, mine does that too. I just clear the code, and it eventually comes back. It has an issue with the EVAP system..... the purge solenoid.

 

Your truck does that white? Haven't heard of that with the older gen 10's. Actually, I didn't know the older models had a gas cap light lol.

But that's correct imo (your post). Either the cap or the purge solenoid. That solenoid rarley goes out on these models, but have. A plugged vent top of the tank (there's two) could also cause a problem. But that's just theory...since it doesn't happen.

The older models get a solenoid or canister DTC. Newer models (gen 10's) have different set ups. Since Ford quit offering canister replacements, the DTC is handled another way by modifying the canister hose. But yea, that's just for our model year trucks.

 

I had this problem on my '97. I ended up replacing the rubber hose between the gas cap and the tank. I guess they can dry out.

 

Yeah, mine has been doing it for about a year. I keep meaning to replace the purge solenoid, but since I don't drive it much (3 or 4 times a month) it's not a priority.

 

I changed the purge solenoid about 2 months ago. I was thinking dropping the tank and checking the lines. Is there a way to check to see if the lines are plugged or to clean them?