I chewed on this long enough, time for the experts to have a bash
Hyundai Elantra SE (“sedan”?), 2009, manual - after the dealer replaced the brake light switch (or some such) as a recall service, soon after - but perhaps unrelated - the cruise control doesn’t work at all from the driver controls. No nothing. All of a sudden. I read about the relays, fuses, however didn’t make much of it - overlooked perhaps… Hoping someone had this exact problem.
… The next step for me is to pay to have someone - dealer or otherwise - rummage around searching for clues. Unless something becomes clear…
The first step is to check if the brake lights actually come on when the cruise control refuses to work.
It passed inspection and I assume they do, but I’ll try to look at the brake lights while the CC button is pressed and such
It may be related to the brake light switch. When you step on the brake pedal, the cruise control is deactivated. I had a brake light switch short so the brake lights were always on. The cruise control then wouldn’t come on. Check and see if your brake lights are always on.
Same thing happened to me (VW Passat) after the dealer replaced the brake light switch on a recall.
they left off a wire or something similar. Took it back and they fixed it.
Since it is a manual trans there is probably a switch on the clutch also.
The safety switches on the pedals is a common and simple problem to fix. There may be a separate switch or contacts used for the CC circuit. If there is a separate switch on the brake pedal it may just need adjustment.
I had the same brake light switch recall performed in 2014 on my 2010 Kia Forte SX manual (a first cousin of your Elantra). I rarely use cruise control but mine worked fine a couple weeks ago. I’m not familiar with your Hyundai dealer. If they are anything like my Kia dealer I’m sure they will re-check your brake light switch installation for free.
looking in the engine bay, there’s a thin-ish box on the left. Real obvious. on top. there’s a rod extending from this thin box to somewhere in the fuel injection assembly on the top of the engine. again, real obvious, rod is sitting there saying hello to the world.
there is a palm-sized wire harness that plugs into the thin box. if it is not plugged in, it can dangle close to the timing belt. also pretty obvious - although it is black, with a black cable, so it can be camouflaged dangling down in the dark corner of the engine.
the wire harness was not plugged in.
to recap : cruise-control box in the engine bay did not have the wire harness plugged in. Plug the wire harness in until it makes a small “snap” sound.
that is all.