I bought a new to me '99 dodge caravan last year. Everything was fine until I broke the gas cap off and bought a new one. When the gas cap broke, the check engine light came on and has been on ever since. I have a friend who has cleared the codes a few times but after a while it will come back on…pardon my lack of proper car terminology…
Are you sure the new gas cap fits properly?
Perhaps the code that comes on is something other than a gas cap warning. Have someone read the code, it will be Pxxx, and post it here.
Unless we know which code is being stored we’re all just guessing.
Have your friend turn off the Check Engine light. Then remove the gas cap and apply a thin coat of petroleum jelly to the seal on the gas cap and reinstall it. If this prevents the Check Engine light from coming on, that new gas cap is leaking.