My "new" 2004 vehicle came with 2 keys.

One is fully functional, the other was labelled "spare".

The spare key works to open the door manually and starts the car, tuning the radio to a different station from the main key. Remotely, it does nothing.
I've replaced its battery, and kept the old one as a spare because it measured OK. The little red light on the key flashes as expected when any button is pressed.

Is there some magic incantation to get this working, or is it a question of throwing cash at a replacement?

Sounds like the spare key may not be synchronised to the car.

There is a method of doing it so the search is your friend.

Search for "sync spare key"

Mike

Thanks for that. The keys are now sync'd after a few passes through the procedure with both keys.

Incidentally, a Google search threw up different instructions. The ones here said front doors closed and unlocked, others said closed and locked. I got it working with the doors unlocked. I wasn't brave enough to try again with the doors locked (as per instructions from RSW Solutions).

I now have to try to sync the 2 seat settings. When the spare key became operative, I thought I was going to be crushed to death. The previous owner of this key must have had extremely short legs.