I have seen al the posts where fan speeds 1, 2, and 3 stop working and it keeps being the resistor and that makes perfect sense to me. But what about in a case where 1, 2, and 4 stop working, but 3 is fine. I would think if this was the resistor it would be in succession of lowest to highest and so 4 would be the last to quit and/or always work while 1, 2, & 3 do not (Isn’t 4 the speed that bypasses the resistor?). Or can it be any combo of speeds that will quit if the resistor starts acting up?
It could also be the control switch itself is going bad. Can’t form a proper guess without vehicle details.
Sounds like the switch or a poor connection somewhere.