I just joined here minutes ago so if this is the wrong forum please move it to where it should be.
On my 2005 class C motorhome with 5.4 liter engine , the gas cap light came on while driving today. I have tried cleaning the seal which is in excellent condition as well as the seat but it didn't help . A friend suggested I should try removing and re-installing the negative lead of the battery to re-set the computer but have not tried that yet . Could the gas cap be defective in spite of it sealing properly ?
Any suggestions on making the light on the dash go out would be welcome

 

The cap could be fine, but it would be a good move to look under the vehicle where the fill piping is located. Some vehicles rust there and exhibit the same symptoms as a defective gas cap, might want to check all the piping under there.