One Key Starts, Two Others Don't

Question

As of yesterday, my wife's key no longer starts our 2002 Hyundai Santa Fe. The key turns fine, all electrical accessories work, but the starter is never engaged. My key (an original) works fine. I have another spare key (also a copy, like my wife's) that acts the same as my wife's.

Battery, starter, solenoid and fuses have all been checked (before it was narrowed down to the key). Both my wife's key and the spare key are > 5 years old, and my wife's has been used near-daily without any issues until yesterday. Not believing it wasn't just some sort of fluke, I repeatedly tried her key and then mine for 15 or 20 times with the same results.

These don't appear to be one of those new-fangled smart keys that everyone seems to have issues with. My wife's and my spare key don't have a rubber head, and are just regular keys. The Santa Fe does have a factory anti-theft system, but we haven't used it in years (the key fobs ate batteries too fast for my tastes) and no longer even carry the fobs.

Easy answer would seem to be that her key is "worn down" somehow (visual inspection doesn't offer any clues) - but with the spare key not working, is it possibly something in the ignition switch or key cylinder? Any other possibilities?

Answer 1

The keys don't necessarily need a rubber head to be 'smart keys', some embed a small resistor inside of them that isn't very noticeable. The fact that the cylinder turns at all means the grooves aren't too worn, etc. It either matches the lock wafers or it doesn't.

I would look online for a programming method for new keys. It's likely that the battery went dead or otherwise lost its key programming. Usually the instructions will be something like putting the good key to ON (but not starting it) and back to OFF 5x, then putting the new key in and starting it (last time I did this was for a remote starter in a Mercury Sable).

Answer 2

if the key can unlock a door, but cannot start the car (while another key can), it is most likely a security mechanism in the key and/or keyfob (real/original one). I have first (and second hand) experience of this happening in Honda Odyssey's (i think it was a 2002).