My S80 Volvo car check engine light is on, i used OBDII device to test, it shows code P0305 cylinder 5 misfire detected, then i found the issue is indeed from spark plug. after i change the spark plug, i used OBDII device to delete code, is this not correct? i am told i should not do anything, the car will remove it automatically. now the thing is i don't know if it is really fixed or not, because the check engine light is not on any more, is it fixed? or it is because i removed the error code? thanks.

 

Yes always delete codes, unless you are taking the car to get fixed and someone else needs to see them. The check engine light will go out if all codes are erased.

If a problem still exists the code will come back. And some codes won't erase by themselves - SRS codes are an example of that.