Symptoms of a failing Fuel Cap
Check engine warning light comes on
If the fuel cap is at all compromised, it won’t be able to trap all of the vapors in the fuel tank. That will disrupt the car’s evaporative emissions system, which may illuminate the check engine light on your dashboard.
Of all the things that can cause your check engine light to come on, this is probably one of the most simple thing. Check to see if it your fuel cap is screwed on tightly. If the light persists, then you might just need a new fuel cap.
Fuel cap warning light
Many modern cars have a fuel cap warning light, to alert you when the fuel cap isn’t fastened. Now, if the light is on, chances are you just forgot to put the fuel cap on.
But if you did put on the fuel cap, and the light is still on, it’s probably because the cap has lost some threading and isn’t properly secured. That means it’s time for a new one.
Cap won’t screw on properly
Similarly, you may notice the fuel cap failing to fasten correctly. When you go to put your fuel cap back on, it may never feel tight, and it might not make the clicking noise that tells you it’s fastened and secured.
If that happens, don’t just ignore it and forget about it. Do something about it.
Car smells of gas
Look, some people are weird and like the smell of raw fuel. They really enjoy gassing up their car for that reason. No judgement here if that's you.
But it shouldn’t happen when the car is driving. If you smell raw gasoline from inside your car, then you may have a fuel cap issue, and it should be addressed.