I have an old Ford Focus car (2003) and for the past 2-3 years, I had the check engine light coming in once a month with a EVAP small leak or very small leak. I already replaced the canister, switch and gas cap without luck. I was prepared to replace the hose and the valve.
Then, my exhaust system started being noisy (I knew it was about to give up) so I had a friend replace the whole thing (excluding catalytic converter). Two months later, the EVAP code has never reappeared. is there a relationship between EVAP and exhaust?
No functional relationship that I'm aware of.
They may share a wiring loom underneath the car though.
Think about it, from the cats to the tailpipe it is just pipe, resonator, and muffler. Nope, no connection between the two, it's just a coincidence, the evap code will eventually come back.
The is a perfect example of why you don't fix problems by just changing parts without diagnosing. You don't actually know if you fixed it.
If you are lucky, then all those parts you changed DID actually fix the problem. But trouble lights don't go out by themselves right away. The computer needs to run tests. If you never reach the conditions to complete the tests (could be a certain speed, or temperature, or whatever) , then it could take many many driving cycles before the computer realizes the problem isn't there any more.
We started with the gas cap, and still the code. Then we did the canister and still the code. If I remember well, there is a switch near the canister. Still the code. The last remaining things to change is the hose and a valve I believe. I could change them but the code is really more an annoyance than a real trouble as a Ford dealer told me last year.
I also replaced the starter. Actually, it was the starter wire that was corroded but since we had to remove it anyways, we put a new starter in. However, I assume that the EVAP system must be connected to the fuse box. I can’t explain why the EVAP code just vanished. After two months, it is very surprising already but maybe it is just some kind of luck that I am having.